fix bad mem access in bb64 decode routine

fix bad mem access (found with valgrind), the fix is adapted
from Cinder's bug fix for this issue in their copy of bb64, see:
 cinder/Cinder#1555

(note: bb64 is public domain and Cinder is BSD-2)

src/tests/conduit/t_conduit_json_sanitize.cpp

@@ -155,5 +155,9 @@ TEST(conduit_json_sanitize, simple_quoteless_schema)
     EXPECT_EQ(n5["top"][2].as_uint32(),d_val);
     EXPECT_EQ(n5["other"].as_float64(),e_val);
 
+    delete [] data;
+    delete [] data2;
+    delete [] data3;
+    delete [] data4;
 }
 

src/thirdparty_builtin/libb64-1.2.1/src/cdecode.c

@@ -48,7 +48,12 @@ int base64_decode_block(const char* code_in, const int length_in, char* plaintex
 				if (codechar == code_in+length_in)
 				{
 					state_in->step = step_a;
-					state_in->plainchar = *plainchar;
+                    // fix bad mem ref (found with valgrind)
+                    // this fix is adapted from Cinder's bug fix for this issue in 
+                    // their copy of bb64, see:
+                    //   https://github.com/cinder/Cinder/pull/1555
+                    // (note: bb64 is public domain and Cinder is BSD-2)
+					state_in->plainchar = 0;
 					return plainchar - plaintext_out;
 				}
 				fragment = (char)base64_decode_value(*codechar++);