output-json-email: fix memleak

This patch fixes some error handling in code generating JSON output for
email event.

This fixes:

Indirect leak of 128 byte(s) in 1 object(s) allocated from:
    #0 0x50c142 in malloc (/home/eric/git/oisf/src/.libs/lt-suricata+0x50c142)
    #1 0x7ff92394771c  (/usr/lib/x86_64-linux-gnu/libjansson.so.4+0x371c)
    #2 0x1bd3309 in JsonEmailLogJson /home/eric/git/oisf/src/output-json-email-common.c:376:19
    #3 0x1bfe774 in JsonSmtpLogger /home/eric/git/oisf/src/output-json-smtp.c:103:9
    #4 0x1c378ff in OutputTxLog /home/eric/git/oisf/src/output-tx.c:165:17
    #5 0x1f94ef3 in TmThreadsSlotVarRun /home/eric/git/oisf/src/tm-threads.c:134:17
    #6 0x1d33478 in TmThreadsSlotProcessPkt /home/eric/git/oisf/src/./tm-threads.h:150:9
    #7 0x1d32dd4 in PcapFileCallbackLoop /home/eric/git/oisf/src/source-pcap-file.c:184:9
    #8 0x7ff924199013  (/usr/lib/x86_64-linux-gnu/libpcap.so.0.8+0x1f013)

Indirect leak of 96 byte(s) in 3 object(s) allocated from:
    #0 0x50c142 in malloc (/home/eric/git/oisf/src/.libs/lt-suricata+0x50c142)
    #1 0x7ff92394bc7b  (/usr/lib/x86_64-linux-gnu/libjansson.so.4+0x7c7b)

Indirect leak of 82 byte(s) in 3 object(s) allocated from:
    #0 0x50c142 in malloc (/home/eric/git/oisf/src/.libs/lt-suricata+0x50c142)
    #1 0x7ff923949924  (/usr/lib/x86_64-linux-gnu/libjansson.so.4+0x5924)

Indirect leak of 72 byte(s) in 1 object(s) allocated from:
    #0 0x50c142 in malloc (/home/eric/git/oisf/src/.libs/lt-suricata+0x50c142)
    #1 0x7ff92394bcda in json_object (/usr/lib/x86_64-linux-gnu/libjansson.so.4+0x7cda)
    #2 0x1bd3309 in JsonEmailLogJson /home/eric/git/oisf/src/output-json-email-common.c:376:19
    #3 0x1bfe774 in JsonSmtpLogger /home/eric/git/oisf/src/output-json-smtp.c:103:9
    #4 0x1c378ff in OutputTxLog /home/eric/git/oisf/src/output-tx.c:165:17
    #5 0x1f94ef3 in TmThreadsSlotVarRun /home/eric/git/oisf/src/tm-threads.c:134:17
    #6 0x1d33478 in TmThreadsSlotProcessPkt /home/eric/git/oisf/src/./tm-threads.h:150:9
    #7 0x1d32dd4 in PcapFileCallbackLoop /home/eric/git/oisf/src/source-pcap-file.c:184:9
    #8 0x7ff924199013  (/usr/lib/x86_64-linux-gnu/libpcap.so.0.8+0x1f013)

Indirect leak of 64 byte(s) in 1 object(s) allocated from:
    #0 0x50c142 in malloc (/home/eric/git/oisf/src/.libs/lt-suricata+0x50c142)
    #1 0x7ff92394bf5a in json_array (/usr/lib/x86_64-linux-gnu/libjansson.so.4+0x7f5a)
    #2 0x1bd04b5 in JsonEmailLogJsonData /home/eric/git/oisf/src/output-json-email-common.c:296:27
    #3 0x1bd3309 in JsonEmailLogJson /home/eric/git/oisf/src/output-json-email-common.c:376:19
    #4 0x1bfe774 in JsonSmtpLogger /home/eric/git/oisf/src/output-json-smtp.c:103:9
    #5 0x1c378ff in OutputTxLog /home/eric/git/oisf/src/output-tx.c:165:17
    #6 0x1f94ef3 in TmThreadsSlotVarRun /home/eric/git/oisf/src/tm-threads.c:134:17
    #7 0x1d33478 in TmThreadsSlotProcessPkt /home/eric/git/oisf/src/./tm-threads.h:150:9
    #8 0x1d32dd4 in PcapFileCallbackLoop /home/eric/git/oisf/src/source-pcap-file.c:184:9
    #9 0x7ff924199013  (/usr/lib/x86_64-linux-gnu/libpcap.so.0.8+0x1f013)

Indirect leak of 48 byte(s) in 1 object(s) allocated from:
    #0 0x50c142 in malloc (/home/eric/git/oisf/src/.libs/lt-suricata+0x50c142)
    #1 0x7ff92394bf2a in json_array (/usr/lib/x86_64-linux-gnu/libjansson.so.4+0x7f2a)
    #2 0x1bd04b5 in JsonEmailLogJsonData /home/eric/git/oisf/src/output-json-email-common.c:296:27
    #3 0x1bd3309 in JsonEmailLogJson /home/eric/git/oisf/src/output-json-email-common.c:376:19
    #4 0x1bfe774 in JsonSmtpLogger /home/eric/git/oisf/src/output-json-smtp.c:103:9
    #5 0x1c378ff in OutputTxLog /home/eric/git/oisf/src/output-tx.c:165:17
    #6 0x1f94ef3 in TmThreadsSlotVarRun /home/eric/git/oisf/src/tm-threads.c:134:17
    #7 0x1d33478 in TmThreadsSlotProcessPkt /home/eric/git/oisf/src/./tm-threads.h:150:9
    #8 0x1d32dd4 in PcapFileCallbackLoop /home/eric/git/oisf/src/source-pcap-file.c:184:9
    #9 0x7ff924199013  (/usr/lib/x86_64-linux-gnu/libpcap.so.0.8+0x1f013)

src/output-json-email-common.c

@@ -253,6 +253,7 @@ json_t *JsonEmailLogJsonData(const Flow *f, void *state, void *vtx, uint64_t tx_
             smtp_state = (SMTPState *)state;
             if (smtp_state == NULL) {
                 SCLogDebug("no smtp state, so no request logging");
+                json_decref(sjs);
                 SCReturnPtr(NULL, "json_t");
             }
             SMTPTransaction *tx = vtx;
@@ -262,6 +263,7 @@ json_t *JsonEmailLogJsonData(const Flow *f, void *state, void *vtx, uint64_t tx_
             break;
         default:
             /* don't know how we got here */
+            json_decref(sjs);
             SCReturnPtr(NULL, "json_t");
     }
     if ((mime_state != NULL)) {
@@ -306,8 +308,10 @@ json_t *JsonEmailLogJsonData(const Flow *f, void *state, void *vtx, uint64_t tx_
             }
         }
 
-        if (mime_state->stack == NULL || mime_state->stack->top == NULL || mime_state->stack->top->data == NULL)
+        if (mime_state->stack == NULL || mime_state->stack->top == NULL || mime_state->stack->top->data == NULL) {
+            json_decref(sjs);
             SCReturnPtr(NULL, "json_t");
+        }
 
         entity = (MimeDecEntity *)mime_state->stack->top->data;
         int attch_cnt = 0;