Compiler crash when nested template function doesn't use templated argument

[aneshlya]

This issue was discovered in #2790 (comment).
Nested template (foo2) without templated arguments https://ispc.godbolt.org/z/fe9szMa4v - breaks.
Nested template (foo2) with templated arguments https://ispc.godbolt.org/z/eK8j1bqcq - works.

When function has templated arguments, we check it in ResolveOverloads https://github.com/ispc/ispc/blob/main/src/expr.cpp#L8900 and return earlier before doing AddInstantiation. If not, we continue executing the function and create a new instantiation, but it's too earlier for that.