Fix texture validation logic (#2509)

* fix mip level computation for asmjs and add support for srgb textures in es2/webgl

* fix BX_TRACE in glcontext_html5.cpp

* fix wrong logic in texture validation

Co-authored-by: Sebastian Marketsmueller <sebastianm@hq.unity3d.com>
Co-authored-by: Vladimir Vukicevic <vladimir@pobox.com>

src/glcontext_html5.cpp

@@ -140,7 +140,6 @@ namespace bgfx { namespace gl
 			}
 			error = (int) context;
 		}
-
 		BX_TRACE("Failed to create WebGL context. (Canvas handle: '%s', last attempt error %d)", canvas, error);
 		return NULL;
 	}