gl: use glActiveTexture() instead of glClientActiveTexture() to match

the GLES2 codepath.

src/debugquad.cpp

@@ -178,7 +178,7 @@ void DebugQuad::TickDraw(float deltams)
     glEnableVertexAttribArray(attr_tex);
 
     /* Bind texture */
-    glClientActiveTexture(GL_TEXTURE0);
+    glActiveTexture(GL_TEXTURE0);
     glBindTexture(GL_TEXTURE_2D, data->texlist[0]);
 
     glBindBuffer(GL_ARRAY_BUFFER, data->buflist[0]);

src/tileset.cpp

@@ -171,7 +171,7 @@ void TileSet::Bind()
 {
     if (!data->img && data->texture)
     {
-        glClientActiveTexture(GL_TEXTURE0);
+        glActiveTexture(GL_TEXTURE0);
         glBindTexture(GL_TEXTURE_2D, data->texture);
     }
 }