cleanup identical conditions (#1339)

cleanup identical conditions (#1339)

[MagickCore/nt-base.c:1403] -> [MagickCore/nt-base.c:1408]: (warning) Identical inner 'if' condition is always true.
[MagickCore/prepress.c:139] -> [MagickCore/prepress.c:144]: (warning) Identical inner 'if' condition is always true.
[MagickCore/quantize.c:3382] -> [MagickCore/quantize.c:3387]: (warning) Identical inner 'if' condition is always true.
[MagickCore/xml-tree.c:449] -> [MagickCore/xml-tree.c:454]: (warning) Identical inner 'if' condition is always true.
[MagickCore/xml-tree.c:528] -> [MagickCore/xml-tree.c:530]: (warning) Identical inner 'if' condition is always true.
[coders/dds.c:1172] -> [coders/dds.c:1178]: (warning) Identical inner 'if' condition is always true.