Forgot to update state tracker in ARB_multi_bind texture binding impl.

Would cause random weird issues with texture configuration/upload if
ARB_multi_bind is available and EXT_direct_state_access is not. Probably
not an issue, since EXT_direct_state_access is probably available on all
drivers which support also ARB_multi_bind.

src/Magnum/AbstractTexture.cpp

@@ -137,6 +137,8 @@ void AbstractTexture::bindImplementationDefault(GLint textureUnit) {
 
 #ifndef MAGNUM_TARGET_GLES
 void AbstractTexture::bindImplementationMulti(GLint textureUnit) {
+    /* Bind the texture to the unit, update state tracker */
+    Context::current()->state().texture->bindings[textureUnit] = _id;
     glBindTextures(textureUnit, 1, &_id);
 }