Evaluate return of strftime.

Author: daltomi

src/main.c

@@ -623,7 +623,11 @@ im_printf(char *str, struct tm *tm,
   struct stat st;
 
   ret[0] = '\0';
-  strftime(strf, 4095, str, tm);
+
+  if (strftime(strf, 4095, str, tm) == 0) {
+    fprintf(stderr, "strftime returned 0\n");
+    exit(EXIT_FAILURE);
+  }
 
   for (c = strf; *c != '\0'; c++) {
     if (*c == '$') {