minor tweaks

lib/t.c

@@ -190,13 +190,17 @@ if (foo) {
 	return foo;
 	}
 
-fimg_get_minmax_rgb(&dessin, vals);
+foo = fimg_get_minmax_rgb(&dessin, vals);
+if (foo) {
+	fprintf(stderr, "%s: err %d on fimg_get_minmax_rgb\n",
+			__func__, foo);
+	return foo;
+	}
 
 for (foo=0; foo<6; foo++) {
 	fprintf(stderr, "%7d    %17.6g\n", foo, vals[foo]);
 	}
 
-
 return -1;
 }
 /* ---------------------------------------------------------------- */