ABI: restore InputOptions::setLinearTransform(...)

The linear transform has never been implemented, so just add as a stub
for API/ABI compatibility.

Fixes part of https://github.com/castano/nvidia-texture-tools/issues/259

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>

src/nvtt/InputOptions.cpp

@@ -337,6 +337,12 @@ void InputOptions::setNormalizeMipmaps(bool normalize)
     m.normalizeMipmaps = normalize;
 }
 
+// Set linear transform for the given channel.
+// Stub for ABI compatibily, never implemented
+void InputOptions::setLinearTransform(int, float, float, float, float)
+{
+}
+
 void InputOptions::setMaxExtents(int e)
 {
     nvDebugCheck(e > 0);

src/nvtt/nvtt.h

@@ -322,6 +322,9 @@ namespace nvtt
         NVTT_API void setNormalFilter(float sm, float medium, float big, float large);
         NVTT_API void setNormalizeMipmaps(bool b);
 
+        // Set color transforms.
+        NVTT_API void setLinearTransform(int channel, float w0, float w1, float w2, float w3);
+
         // Set resizing options.
         NVTT_API void setMaxExtents(int d);
         NVTT_API void setRoundMode(RoundMode mode);