Metal: avoid crashing for invalid programs (#8321)

Author: bejado

filament/backend/src/metal/MetalContext.h

@@ -155,6 +155,7 @@ struct MetalContext {
 
     RenderPassFlags currentRenderPassFlags;
     MetalRenderTarget* currentRenderTarget = nullptr;
+    bool validPipelineBound = false;
 
     // State trackers.
     PipelineStateTracker pipelineState;

filament/backend/src/metal/MetalDriver.mm

@@ -1657,6 +1657,7 @@
     // during the draw call when the program is invalid. The shader compile error has already been
     // dumped to the console at this point, so it's fine to simply return early.
     if (FILAMENT_ENABLE_MATDBG && UTILS_UNLIKELY(!functions)) {
+        mContext->validPipelineBound = false;
         return;
     }
 
@@ -1789,6 +1790,8 @@
                                                    clamp:0.0];
         mContext->currentPolygonOffset = ps.polygonOffset;
     }
+
+    mContext->validPipelineBound = true;
 }
 
 void MetalDriver::bindRenderPrimitive(Handle<HwRenderPrimitive> rph) {
@@ -1886,6 +1889,10 @@
             << "draw() without a valid command encoder.";
     DEBUG_LOG("draw2(...)\n");
 
+    if (FILAMENT_ENABLE_MATDBG && UTILS_UNLIKELY(!mContext->validPipelineBound)) {
+        return;
+    }
+
     // Bind the offset data.
     if (mContext->dynamicOffsets.isDirty()) {
         const auto [size, data] = mContext->dynamicOffsets.getOffsets();