Fix 3D blit test (#2651)

bi.m_depth == 1 for usual 2D blit

src/renderer_gl.cpp

@@ -7134,7 +7134,7 @@ namespace bgfx { namespace gl
 				const TextureGL& src = m_textures[bi.m_src.idx];
 				const TextureGL& dst = m_textures[bi.m_dst.idx];
 
-				BX_ASSERT(0 == bi.m_srcZ && 0 == bi.m_dstZ && 0 == bi.m_depth
+				BX_ASSERT(0 == bi.m_srcZ && 0 == bi.m_dstZ && 1 >= bi.m_depth
 					, "Blitting 3D regions is not supported"
 					);