avoid request stalls during proactive rebuilds

src/wasm/backend.cpp

@@ -100,7 +100,7 @@ static bool wasm_artifact_exists(Request* context, const String& entry_unit)
 	// metadata mismatches, which can leave stale wasm with old imports.
 	bool source_missing = false;
 	if(compiler_unit_needs_recompile(context, entry_unit, &source_missing))
-		return(false);
+		return(compiler_unit_compile_in_progress(context, entry_unit));
 	if(source_missing)
 		return(false);
 	return(true);

src/wasm/worker.cpp

@@ -1606,7 +1606,7 @@ private:
 			return(1);
 		}
 
-		if(!file_exists_host(worker.unit_wasm_path(resolved)) || compiler_unit_needs_recompile(context, resolved, 0))
+		if(!file_exists_host(worker.unit_wasm_path(resolved)) || (compiler_unit_needs_recompile(context, resolved, 0) && !compiler_unit_compile_in_progress(context, resolved)))
 			get_shared_unit(context, resolved);
 
 		size_t unit_index = 0;