Improve IQM loading

- Only allocate memory for vertex arrays that are present in the IQM
file and are actually used (may not have colors or blend index/weights,
don't load tangents in opengl1). (Colors is fixed to next commit.)
- Explicitly handle loading IQM files without meshes (bones only).
- Better IQM validation. Header data offset 0 mean data is not present
in file. Check if required vertex arrays are present.

This involved a lot of white space changes and moving code around.

code/renderergl1/tr_local.h

@@ -599,6 +599,7 @@ typedef struct {
 	int		num_poses;
 	struct srfIQModel_s	*surfaces;
 
+	int		*triangles;
 	float		*positions;
 	float		*texcoords;
 	float		*normals;
@@ -609,18 +610,17 @@ typedef struct {
 		byte	*b;
 	} blendWeights;
 	byte		*colors;
-	int		*triangles;
 
 	// depending upon the exporter, blend indices and weights might be int/float
 	// as opposed to the recommended byte/byte, for example Noesis exports
 	// int/float whereas the official IQM tool exports byte/byte
 	byte blendWeightsType; // IQM_UBYTE or IQM_FLOAT
 
+	char		*jointNames;
 	int		*jointParents;
 	float		*jointMats;
 	float		*poseMats;
 	float		*bounds;
-	char		*names;
 } iqmData_t;
 
 // inter-quake-model surface