ImageMagick: Memory leak in coders/txt.c without freetype

If a texture attribute is specified for a TXT file, an attempt will be made to read it via texture=ReadImage(read_info,exception);. Later, when retrieving metrics via the GetTypeMetrics function, if this function fails (i.e., status == MagickFalse), the calling function will exit immediately but fail to release the texture object, leading to memory leakage.