Fix UB in memcasemem when no match is found

http-response-bodies.c

@@ -45,6 +45,7 @@ char* memcasemem(char* haystack, size_t haystacklen, char* needle, size_t needle
 			}
 		}
 	}
+	return NULL;
 }
 
 int main(int argc, char* argv[]) {