inotify: Fix a few trivial -Wsign-conversion warnings

When building GIO with `-Wsign-conversion` enabled.

In all of these cases, the implicit sign conversion cast is correct, so
let’s make it explicit to indicate that we‘ve checked it.

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

Helps: #3405

gio/inotify/inotify-helper.c

@@ -260,7 +260,7 @@ ih_not_missing_callback (inotify_sub *sub)
 static GFileMonitorEvent
 ih_mask_to_EventFlags (guint32 mask)
 {
-  mask &= ~IN_ISDIR;
+  mask &= (guint32) ~IN_ISDIR;
   switch (mask)
     {
     case IN_MODIFY:
@@ -287,6 +287,6 @@ ih_mask_to_EventFlags (guint32 mask)
     case IN_ACCESS:
     case IN_IGNORED:
     default:
-      return -1;
+      return (GFileMonitorEvent) -1;
     }
 }

gio/inotify/inotify-kernel.c

@@ -144,7 +144,7 @@ ik_source_can_dispatch_now (InotifyKernelSource *iks,
   return 0 <= dispatch_time && dispatch_time <= now;
 }
 
-static gsize
+static size_t
 ik_source_read_some_events (InotifyKernelSource *iks,
                             gchar               *buffer,
                             gsize                buffer_len)
@@ -169,7 +169,7 @@ again:
   else if (result == 0)
     g_error ("inotify unexpectedly hit eof");
 
-  return result;
+  return (size_t) result;
 }
 
 static gchar *

gio/inotify/inotify-path.c

@@ -482,7 +482,7 @@ ip_event_dispatch (GList      *dir_list,
 	   */
 	  if (sub->hardlinks)
 	    {
-	      event->mask &= ~IP_INOTIFY_FILE_MASK;
+	      event->mask &= (guint32) ~IP_INOTIFY_FILE_MASK;
 	      if (!event->mask)
 		continue;
 	    }