core/unit: don't log 0 values in unit_log_resources

Prompted by systemd#30573

Author: YHNdnzj

src/core/unit.c

@@ -2411,6 +2411,10 @@ static int unit_log_resources(Unit *u) {
                         return log_oom();
                 iovec[n_iovec++] = IOVEC_MAKE_STRING(TAKE_PTR(t));
 
+                /* If value is 0, we don't log it in the MESSAGE= field. */
+                if (v == 0)
+                        continue;
+
                 if (strextendf_with_separator(&message, ", ", "%s %s",
                                               FORMAT_BYTES(v), memory_fields[metric].message_suffix) < 0)
                         return log_oom();
@@ -2434,6 +2438,10 @@ static int unit_log_resources(Unit *u) {
                         return log_oom();
                 iovec[n_iovec++] = IOVEC_MAKE_STRING(TAKE_PTR(t));
 
+                /* If value is 0, we don't log it in the MESSAGE= field. */
+                if (value == 0)
+                        continue;
+
                 /* Format the IO accounting data for inclusion in the human language message string, but only
                  * for the bytes counters (and not for the operations counters) */
                 if (io_fields[k].message_suffix) {
@@ -2461,6 +2469,10 @@ static int unit_log_resources(Unit *u) {
                         return log_oom();
                 iovec[n_iovec++] = IOVEC_MAKE_STRING(TAKE_PTR(t));
 
+                /* If value is 0, we don't log it in the MESSAGE= field. */
+                if (value == 0)
+                        continue;
+
                 /* Format the IP accounting data for inclusion in the human language message string, but only
                  * for the bytes counters (and not for the packets counters) */
                 if (ip_fields[m].message_suffix) {