Fix segfault in imagecopyresized().

Author: Ilia Alshanetsky

ext/gd/gd.c

@@ -2946,6 +2946,11 @@ PHP_FUNCTION(imagecopyresized)
 	dstY = Z_LVAL_PP(DY);
 	dstH = Z_LVAL_PP(DH);
 	dstW = Z_LVAL_PP(DW);
+	
+	if (dstW < 0 || dstH < 0 || srcW < 0 || srcH < 0) {
+		php_error_docref(NULL TSRMLS_CC, E_WARNING, "Invalid image dimensions");
+		RETURN_FALSE;
+	}
 
 	gdImageCopyResized(im_dst, im_src, dstX, dstY, srcX, srcY, dstW, dstH, srcW, srcH);
 	RETURN_TRUE;