Stop fatal error when Parameter#getName returns NULL
Stop fatal error when Parameter#getName returns NULL

For whatever reason, if you remove the "$" before a variable and
attempt to goto definition for that parameter, the SymbolContextResolver
causes a FatalError when passing the NULL value to the collection has()
method.

Cannot reproduce this in WR with tests.

Fixes #533

dantleech/worse-reflection,dantleech/worse-reflection