Sema: Fix logic error in TypeChecker::typeCheckPattern()
Sema: Fix logic error in TypeChecker::typeCheckPattern()

Use overwriteType() instead of setType() because we can end up with
a type here if the pattern was previously marked invalid.

I don't have a test for this, but its needed to fix some
compiler_crashers regressions with upcoming patches.

khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift