Instead of calling 'MagickWandGenesis' every time an image is loaded, only
call it the first time, and similarly do not call 'MagickWandTerminus' if
the library has not been used before.
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
- changed header used for MagickWand to the one specified in the online
documentation
- changed a comparison to 'MagickTrue' because its value does not allow a
compiler optimisation that would be expected in present case
- fixed potential crash, if loading with Magick fails it could return a
pointer to a de-allocated area
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>