Make sure unmap chunk isn't lost and goes in buffer record

* If we're ignoring a map it's marked correctly as dirty, but otherwise a
  buffer could be mapped once then not touched, not become dirty, and so
  we need the unmap chunk in its record.

renderdoc/driver/gl/wrappers/gl_buffer_funcs.cpp

@@ -1452,7 +1452,9 @@ GLboolean WrappedOpenGL::glUnmapNamedBufferEXT(GLuint buffer)
 				}
 				else
 				{
+					SCOPED_SERIALISE_CONTEXT(UNMAP);
 					Serialise_glUnmapNamedBufferEXT(buffer);
+					record->AddChunk(scope.Get());
 				}
 				
 				break;