resolve several null pointer dereferences

resolve several null pointer dereferences
found by cppcheck

[MagickCore/draw.c:881] -> [MagickCore/draw.c:879]: (warning) Either the condition 'draw_info!=(DrawInfo*)NULL' is redundant or there is possible null pointer dereference: draw_info.
[MagickCore/fx.c:3966] -> [MagickCore/fx.c:3964]: (warning) Either the condition 'image!=(Image*)NULL' is redundant or there is possible null pointer dereference: image.
[MagickCore/fx.c:5009] -> [MagickCore/fx.c:5006]: (warning) Either the condition 'right_image!=(const Image*)NULL' is redundant or there is possible null pointer dereference: right_image.
[MagickCore/montage.c:168] -> [MagickCore/montage.c:166]: (warning) Either the condition 'montage_info!=(MontageInfo*)NULL' is redundant or there is possible null pointer dereference: montage_info.
[MagickCore/montage.c:416] -> [MagickCore/montage.c:415]: (warning) Either the condition 'master_list==(Image**)NULL' is redundant or there is possible null pointer dereference: image_list.
[MagickCore/nt-base.c:1792] -> [MagickCore/nt-base.c:1797]: (warning) Either the condition 'entry!=(DIR*)NULL' is redundant or there is possible null pointer dereference: entry.
[MagickWand/drawing-wand.c:177] -> [MagickWand/drawing-wand.c:175]: (warning) Either the condition 'wand!=(DrawingWand*)NULL' is redundant or there is possible null pointer dereference: wand.
[MagickWand/drawing-wand.c:4540] -> [MagickWand/drawing-wand.c:4538]: (warning) Either the condition 'wand!=(DrawingWand*)NULL' is redundant or there is possible null pointer dereference: wand.
[MagickWand/drawing-wand.c:4682] -> [MagickWand/drawing-wand.c:4680]: (warning) Either the condition 'wand!=(DrawingWand*)NULL' is redundant or there is possible null pointer dereference: wand.
[coders/msl.c:575] -> [coders/msl.c:555]: (warning) Either the condition 'image==(Image*)NULL' is redundant or there is possible null pointer dereference: image.