Fix ReplaceUninitializedStringPhis.

Move the analysis after redundant phi and dead phi elimination,
knowing that only graphs with irreducible loops may still have
a phi as input of the invoke. In such a case, we bail.

bug: 112537407
Test: 563-checker-fake-string
Change-Id: Ib9eefa4ce905b7fb418ca9b2a3c26ea4df74ce8f