bool = pfont:IsNull()
True if the font is NULL, i.e. invalid. If functions
that allocate fonts fail, they might not throw an error but simply set the
font to NULL. You can use this function to check if font allocation has
failed in which case the font will be NULL.
Also, certain getter functions can return a NULL object in case the object
doesn't exist. You can use this function to check if a getter function returned
a NULL handle.
True if the font is NULL, otherwise False