Fuse.Drawing.Surface: avoid out-of-memory exception
Fuse.Drawing.Surface: avoid out-of-memory exception

It seems the .NET implementation of LinearGradientBrush doesn't really
like zero-length gradients, so we end up allocating a silly amount of
memory, eventually crashing.

We already have an early-out like this earlier, so let's add one more
to avoid crashing.

Fixes #1117.

fusetools/fuselibs-public,fusetools/fuselibs-public,nekronos/fuselibs-public,cbaggers/fuselibs-public,nekronos/fuselibs-public,kusma/fuselibs-public,cbaggers/fuselibs-public,cbaggers/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,fusetools/fuselibs-public,fusetools/fuselibs-public,kusma/fuselibs-public,kusma/fuselibs-public,nekronos/fuselibs-public,kusma/fuselibs-public,cbaggers/fuselibs-public,cbaggers/fuselibs-public,kusma/fuselibs-public,nekronos/fuselibs-public,fusetools/fuselibs-public,nekronos/fuselibs-public,kusma/fuselibs-public,fusetools/fuselibs-public,nekronos/fuselibs-public,cbaggers/fuselibs-public,cbaggers/fuselibs-public,nekronos/fuselibs-public