Fix uninitialized memory use with -MT and -MQ

This didn't break unless the first uninitialized byte was non-zero,
which happened to be the case on someone's Windows machine.

Would it be worth it setting up Valgrind in CI?

src/asm/main.c

@@ -454,7 +454,6 @@ int main(int argc, char *argv[])
 
 		/* Long-only options */
 		case 0:
-			if (depType) {
 			switch (depType) {
 			case 'G':
 				oGeneratedMissingIncludes = true;
@@ -472,9 +471,16 @@ int main(int argc, char *argv[])
 					ep = make_escape(ep);
 
 				nTargetFileNameLen += strlen(ep) + 1;
+				if (!tzTargetFileName) {
+					/* On first alloc, make an empty str */
+					tzTargetFileName =
+						malloc(nTargetFileNameLen + 1);
+					*tzTargetFileName = '\0';
+				} else {
 					tzTargetFileName =
 						realloc(tzTargetFileName,
 							nTargetFileNameLen + 1);
+				}
 				if (tzTargetFileName == NULL)
 					err(1, "Cannot append new file to target file list");
 				strcat(tzTargetFileName, ep);
@@ -486,7 +492,6 @@ int main(int argc, char *argv[])
 				*ptr = '\0';
 				break;
 			}
-			}
 			break;
 
 		/* Unrecognized options */