fix option handling in Makefile.PL when libgd-dev is not installed

the call to GetOptions() must be unique.

before fix:

    $ perl Makefile.PL -options=PNG,FT -ignore_missing_gd
    Unknown option: options

    Where is libgd installed? [/usr/lib]

    Please choose the features that match how libgd was built:
    Build JPEG support? [y]
    Build PNG support? [y]
    Build FreeType support? [y]
    Build GIF support? [y]
    Build support for animated GIFs? [y]
    Build XPM support? [y]

with fix:

    $ perl Makefile.PL -options=PNG,FT -ignore_missing_gd
    Included Features:          PNG,FT

    Where is libgd installed? [/usr/lib]