mesa: move _mesa_debug() call earlier in _mesa_Scissor

Part of a patch from Xavier Chantry <chantry.xavier@gmail.com>
diff --git a/src/mesa/main/scissor.c b/src/mesa/main/scissor.c
index b5f4cde..523f3c3 100644
--- a/src/mesa/main/scissor.c
+++ b/src/mesa/main/scissor.c
@@ -37,14 +37,14 @@
    GET_CURRENT_CONTEXT(ctx);
    ASSERT_OUTSIDE_BEGIN_END(ctx);
 
+   if (MESA_VERBOSE & VERBOSE_API)
+      _mesa_debug(ctx, "glScissor %d %d %d %d\n", x, y, width, height);
+
    if (width < 0 || height < 0) {
       _mesa_error( ctx, GL_INVALID_VALUE, "glScissor" );
       return;
    }
 
-   if (MESA_VERBOSE & VERBOSE_API)
-      _mesa_debug(ctx, "glScissor %d %d %d %d\n", x, y, width, height);
-
    _mesa_set_scissor(ctx, x, y, width, height);
 }