Change various types to the correct signedness to avoid warnings.

Also cast the check of "inet_addr" to guint32. The POSIX declaration
of this function returns in_addr_t which is the same as uint32_t.
Windows does not define this type and instead uses unsigned long.

plugins/fishlim/fish.c

@@ -145,7 +145,8 @@ void fish_deinit(void)
  */
 char *fish_base64_encode(const char *message, size_t message_len) {
     BF_LONG left = 0, right = 0;
-    int i, j;
+    int i;
+    size_t j;
     char *encoded = NULL;
     char *end = NULL;
     char *msg = NULL;