[SemaExpr] Re-enable missing assertion.
[SemaExpr] Re-enable missing assertion.

This has been disabled for a long time, but:
1) Initializers work (and apparently they're re reason why this was disabled).
2) various tests happen to hit this code path and the invariant seems to be
always verified.

Differential Revision:	http://reviews.llvm.org/D12110
Reviewed by:	rsmith


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@245404 91177308-0d34-0410-b5e6-96231b3b80d8

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