This commit fixes a panic which can happen on a module with an invalid
name section where one of the functions named has the index `u32::MAX`.
Previously Wasmtime would create a new `FuncIndex` with the indices
found in the name section but the sentinel `u32::MAX` causes a panic.
Cranelift otherwise limits the number of functions through `wasmparser`
which has a hard limit (lower than `u32::MAX`) so this commit applies a
fix of only recording function names for function indices that are
actually present in the module.
6be0f82b96