gskngltexturelibraryprivate.h: Fix build on Visual Studio

The 'GskNglTextureAtlasEntry' structure is used as a member in two other
structures in two Gsk private headers, namely 'GskNglGlyphValue' and
'GskNglIconData', but the build breaks on Visual Studio since
'GskNglTextureAtlasEntry' contains a last member that is a zero-sized array
that is normally OK if it is the last member of structure -or- if the structure
that contains a 'GskNglTextureAtlasEntry' structure as its last member.
Otherwise, a GCCism is involved here.

Fix the build on Visual Studio compilers by not using a zero-sized array as
a last member of 'GskNglTextureAtlasEntry', on Visual Studio compilers.
12 jobs for fix.ngl.msvc in 11 minutes and 23 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  .Pre
failed #1184102
allowed to fail
style-check-diff

00:03:33

 
  Build
passed #1184103
fedora-x86_64

00:05:40

passed #1184105
installed-tests

00:07:35

passed #1184107
macos
macos

00:11:21

passed #1184106
win32-ps
msys2-mingw64

00:05:46

passed #1184104
release-build

00:07:30

 
  Analysis
failed #1184109
asan allowed to fail
asan-build

00:05:00

passed #1184108
static-scan

00:09:43

 
  Docs
passed #1184110
reference

00:08:10

 
  Flatpak
manual #1184111
flatpak allowed to fail manual
flatpak-manual:demo
manual #1184113
flatpak allowed to fail manual
flatpak-manual:icon-browser
manual #1184112
flatpak allowed to fail manual
flatpak-manual:widget-factory
 
Name Stage Failure
failed
asan-build Analysis
 - css: 214 total, 212 pass, 2 fail
Processing gtk suite a11y:
- a11y: 22 total, 20 pass, 2 fail
Processing gtk suite tools:
- tools: 4 total, 3 pass, 1 fail
Processing gtk suite reftest:
- reftest: 134 total, 129 pass, 5 fail
Cleaning up file based variables
ERROR: Job failed: exit code 1
failed
style-check-diff .Pre
+#define NGL_TRAILING_DATA_SIZE 1
#else
-# define NGL_TRAILING_DATA_SIZE 0
+#define NGL_TRAILING_DATA_SIZE 0
#endif

typedef struct _GskNglTextureAtlasEntry
Cleaning up file based variables
ERROR: Job failed: exit code 1