Fix some LGTM errors of "Multiplication result converted to larger type"

platform/javascript/audio_driver_javascript.cpp

@@ -117,14 +117,15 @@ Error AudioDriverJavaScript::init() {
 	if (output_rb) {
 		memdelete_arr(output_rb);
 	}
-	output_rb = memnew_arr(float, buffer_length *channel_count);
+	const size_t array_size = buffer_length * (size_t)channel_count;
+	output_rb = memnew_arr(float, array_size);
 	if (!output_rb) {
 		return ERR_OUT_OF_MEMORY;
 	}
 	if (input_rb) {
 		memdelete_arr(input_rb);
 	}
-	input_rb = memnew_arr(float, buffer_length *channel_count);
+	input_rb = memnew_arr(float, array_size);
 	if (!input_rb) {
 		return ERR_OUT_OF_MEMORY;
 	}