Fix for fuzzer-discovered error with invalid var-initializers.

If a VarDeclaration line contained multiple variables, and the first
variable had an illegal initializer-expression, the Declare() would
return a Nop. AddVarDeclaration did not expect to see a Nop and would
assert once we tried to process the second var-declaration. Now, we
allow adding var declarations to a Nop.

Bulked up some tests to cover local and global variables (since those
are parsed in separate functions) and to check both the first
initializer as well as follow-on initializers (since those are parsed in
separate parts of the var-decl handler).

Change-Id: I66341191698175b490a659715cb8edaafe2f75ae
Bug: oss-fuzz:39032
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/452696
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
8 files changed