swr/rast: early exit on empty triangle mask

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>

src/gallium/drivers/swr/rasterizer/core/binner.cpp

@@ -1027,6 +1027,12 @@ void SIMDCALL BinTrianglesImpl(DRAW_CONTEXT*          pDC,
 endBinTriangles:
 
 
+    if (!triMask)
+    {
+        RDTSC_END(FEBinTriangles, 1);
+        return;
+    }
+
     // Send surviving triangles to the line or point binner based on fill mode
     if (rastState.fillMode == SWR_FILLMODE_WIREFRAME)
     {