one more parameter check for hdrfilm

src/films/hdrfilm.cpp

@@ -236,6 +236,9 @@ public:
 		if (pixelFormats.size() != 1 && channelNames.size() != pixelFormats.size())
 			Log(EError, "Number of channel names must match the number of specified pixel formats!");
 
+		if (m_pixelFormats.size() != 1 && m_fileFormat != Bitmap::EOpenEXR)
+			Log(EError, "General multi-channel output is only supported when writing OpenEXR files!");
+
 		for (size_t i=0; i<pixelFormats.size(); ++i) {
 			std::string pixelFormat = pixelFormats[i];
 			std::string name = i < channelNames.size() ? (channelNames[i] + std::string(".")) : "";