m.nviz.image: Fix write_img return

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@72951 15284696-431f-4ddb-bdfa-cd5b030d7da7

misc/m.nviz.image/write_img.c

@@ -30,10 +30,10 @@
 int write_img(const char *name, int format)
 {
     if (format == FORMAT_PPM)
-	return !GS_write_ppm(name);
+	return GS_write_ppm(name);
 #ifdef HAVE_TIFFIO_H
     else if (format == FORMAT_TIF)
-	return !GS_write_tif(name);
+	return GS_write_tif(name);
 #endif
     else
 	return 2;