Bug 573473 - [GTK3] ImageLoader.getImageFormat(long) leaks native memory

This change adds the missing OS.g_free() call to
ImageLoader.getImageFormat(), in order to free memory allocated with
GDK.gdk_pixbuf_format_get_name(). This prevents a native memory leak.

Change-Id: I3ff6ae1a6bfe63ea4ac6d3f092ed134d669d3201
Signed-off-by: Simeon Andreev <simeon.danailov.andreev@gmail.com>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.swt/+/180519
Tested-by: Platform Bot <platform-bot@eclipse.org>
Reviewed-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Reviewed-by: Andrey Loskutov <loskutov@gmx.de>
diff --git a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/graphics/ImageLoader.java b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/graphics/ImageLoader.java
index 2731c70..ec5d50b 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/graphics/ImageLoader.java
+++ b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/graphics/ImageLoader.java
@@ -338,6 +338,7 @@
 	long format = GDK.gdk_pixbuf_loader_get_format(loader);
 	long name = GDK.gdk_pixbuf_format_get_name(format);
 	String nameStr = Converter.cCharPtrToJavaString(name, false);
+	OS.g_free(name);
 	switch (nameStr) {
 		case "bmp": return SWT.IMAGE_BMP;
 		case "gif": return SWT.IMAGE_GIF;