swpipe: Cleanup, code correction

* Remove error text as giving SetCurrentContext
  a NULL bitmap isn't a critical error.
* Ensure old front buffer is flushed on SetCurrentContext
* Small style fix

src/add-ons/opengl/swpipe/GalliumContext.cpp

@@ -425,7 +425,6 @@ GalliumContext::SetCurrentContext(Bitmap *bitmap, context_id contextID)
 	struct st_api* api = context->api;
 
 	if (!bitmap) {
-		ERROR("%s: Invalid bitmap provided!\n", __func__);
 		api->make_current(context->api, NULL, NULL, NULL);
 		return B_ERROR;
 	}
@@ -435,7 +434,7 @@ GalliumContext::SetCurrentContext(Bitmap *bitmap, context_id contextID)
 
 	if (oldContextID > 0 && oldContextID != contextID) {
 		fContext[oldContextID]->st->flush(fContext[oldContextID]->st,
-			0, NULL);
+			ST_FLUSH_FRONT, NULL);
 	}
 
 	// TODO: WinSysDrawBuffer & WinSysReadBuffer?

src/add-ons/opengl/swpipe/SoftwareWinsys.h

@@ -28,6 +28,7 @@ struct haiku_displaytarget
 	void* data;
 };
 
+
 struct sw_winsys* winsys_connect_hooks();