ref: gl: track current bound texture index in gl_textures array in separate glState field

ref/gl/gl_backend.c

@@ -220,6 +220,7 @@ void GL_CleanUpTextureUnits( int last )
 			pglDisable( glState.currentTextureTargets[i] );
 			glState.currentTextureTargets[i] = GL_NONE;
 			glState.currentTextures[i] = -1; // unbind texture
+			glState.currentTexturesIndex[i] = 0;
 		}
 
 		GL_SetTexCoordArrayMode( GL_NONE );

ref/gl/gl_image.c

@@ -116,6 +116,7 @@ void GL_Bind( GLint tmu, GLenum texnum )
 
 	pglBindTexture( texture->target, texture->texnum );
 	glState.currentTextures[tmu] = texture->texnum;
+	glState.currentTexturesIndex[tmu] = texnum;
 }
 
 /*
@@ -1208,6 +1209,7 @@ static qboolean GL_UploadTexture( gl_texture_t *tex, rgbdata_t *pic )
 
 	// uploading texture into video memory, change the binding
 	glState.currentTextures[glState.activeTMU] = tex->texnum;
+	glState.currentTexturesIndex[glState.activeTMU] = tex - gl_textures;
 	pglBindTexture( tex->target, tex->texnum );
 
 	for( i = 0; i < numSides; i++ )

ref/gl/gl_local.h

@@ -677,6 +677,7 @@ typedef struct
 	int width, height;
 	int		activeTMU;
 	GLint		currentTextures[MAX_TEXTURE_UNITS];
+	GLint		currentTexturesIndex[MAX_TEXTURE_UNITS];
 	GLuint		currentTextureTargets[MAX_TEXTURE_UNITS];
 	GLboolean		texIdentityMatrix[MAX_TEXTURE_UNITS];
 	GLint		genSTEnabled[MAX_TEXTURE_UNITS];	// 0 - disabled, OR 1 - S, OR 2 - T, OR 4 - R

ref/gl/gl_rsurf.c

@@ -803,7 +803,7 @@ void DrawGLPoly( glpoly_t *p, float xScale, float yScale )
 			flConveyorSpeed = (e->curstate.rendercolor.g<<8|e->curstate.rendercolor.b) / 16.0f;
 			if( e->curstate.rendercolor.r ) flConveyorSpeed = -flConveyorSpeed;
 		}
-		texture = R_GetTexture( glState.currentTextures[glState.activeTMU] );
+		texture = R_GetTexture( glState.currentTexturesIndex[glState.activeTMU] );
 
 		flRate = fabs( flConveyorSpeed ) / (float)texture->srcWidth;
 		flAngle = ( flConveyorSpeed >= 0 ) ? 180 : 0;