string-util: add minor optimization to strrstr()

src/basic/string-util.c

@@ -1519,13 +1519,17 @@ char* strrstr_internal(const char *haystack, const char *needle) {
 
         /* Special case: for the empty string we return the very last possible occurrence, i.e. *after* the
          * last char, not before. */
-        if (*needle == 0)
+        if (needle[0] == 0)
                 return (char*) strchr(haystack, 0);
 
+        /* Special case: for single character strings, just use optimized strrchr() */
+        if (needle[1] == 0)
+                return (char*) strrchr(haystack, needle[0]);
+
         for (const char *p = strstr(haystack, needle), *q; p; p = q) {
                 q = strstr(p + 1, needle);
                 if (!q)
-                        return (char *) p;
+                        return (char*) p;
         }
         return NULL;
 }