Fixed 'variabile might be clobbered' warnings

extensions/cairo_io/cairo-image-surface-jpeg.c

@@ -182,7 +182,7 @@ _cairo_image_surface_create_from_jpeg (GInputStream  *istream,
 	guint32                        pixel;
 	unsigned char                 *p_buffer;
 	int                            x;
-	gboolean                       read_all_scanlines = FALSE;
+	volatile gboolean              read_all_scanlines = FALSE;
 	volatile gboolean              finished = FALSE;
 
 	image = gth_image_new ();

extensions/cairo_io/gth-image-saver-jpeg.c

@@ -237,7 +237,7 @@ _cairo_surface_write_as_jpeg (cairo_surface_t  *image,
 	struct jpeg_compress_struct cinfo;
 	struct error_handler_data jerr;
 	guchar            *buf = NULL;
-	guchar            *pixels = NULL;
+	guchar            *pixels;
 	volatile int       quality = 85; /* default; must be between 0 and 100 */
 	volatile int       smoothing = 0;
 	volatile gboolean  optimize = FALSE;

extensions/cairo_io/gth-image-saver-png.c

@@ -165,7 +165,7 @@ _cairo_surface_write_as_png (cairo_surface_t  *image,
 			     char            **values,
 			     GError          **error)
 {
-	int            compression_level;
+	volatile int   compression_level;
 	int            width, height;
 	gboolean       alpha;
 	guchar        *pixels, *ptr, *buf;