gwinhttpvfs: Fall back to wrapped VFS if creating a HTTP file fails

If we fail to create a GWinhttpFile for a URI (for example, because it’s
an invalid URI or is badly encoded), don’t just return NULL. Instead,
fall back to the wrapped VFS which might be able to handle it instead.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Fixes: #1819
10 jobs for 1819-file-for-uri-null in 19 minutes and 49 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #406980
cross-android_api21_arm64

00:01:43

passed #406981
cross-android_api28_arm64

00:01:22

passed #406982
cross-mingw64

00:02:01

passed #406978
debian-stable-x86_64

00:02:12

passed #406977
fedora-x86_64

00:08:13

passed #406979
G_DISABLE_ASSERT

00:02:11

passed #406983
win32
msys2-mingw32

00:13:41

passed #406984
win32
vs2017-x64

00:10:01

 
  Coverage
passed #406985
coverage

00:01:27

77.8%
 
  Analysis
passed #406986
scan-build

00:04:40