Pass range-min/max to ApplyCustomShader

Adding rangeminmax to globals, snippet support and updated docs to match

Fixes bug in replay_output.cpp, causing a crash due to missing texhandle

docs/how/how_custom_visualisation.rst

@@ -79,6 +79,8 @@ There are several constant parameters available, each detailed below with the va
 		int SelectedSample;
 		uvec4 YUVDownsampleRate;
 		uvec4 YUVAChannels;
+		float SelectedRangeMin;
+		float SelectedRangeMax;
 	} RENDERDOC;
 
 In this way you can access the properties as ``RENDERDOC.TexDim`` instead of ``RENDERDOC_TexDim``.
@@ -156,6 +158,23 @@ This variable will be filled out with the selected multisample sample index as c
 
 So for example in a 4x MSAA texture, the valid values are ``0``, ``1``, ``2``, ``3`` to select a sample, or ``-4`` for 'average value'.
 
+
+Selected RangeMin, RangeMax
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. highlight:: c++
+.. code:: c++
+
+	float RENDERDOC_SelectedRangeMin; // hlsl
+	float RENDERDOC_SelectedRangeMax; // hlsl
+
+	uniform int RENDERDOC_SelectedRangeMin; // glsl
+	uniform int RENDERDOC_SelectedRangeMax; // glsl
+
+
+These variables will be filled out with the current Minimum and Maximum values for the Range-selector in the Texture Viewer.
+
+
 Current texture type
 ~~~~~~~~~~~~~~~~~~~~