gio: Fix various implicit conversions from size_t to smaller types

Basically various trivial instances of the following MSVC compiler
warning:
```
../gio/gio-tool-set.c(50): warning C4267: '=': conversion from 'size_t' to 'int', possible loss of data
```

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

gio/gdbusdaemon.c

@@ -543,7 +543,8 @@ match_matches (GDBusDaemon *daemon,
 {
   MatchElement *element;
   Name *name;
-  int i, len, len2;
+  int i;
+  size_t len, len2;
   const char *value;
   int check_type;