[analyzer] Fix assert in ExprEngine::processSwitch

This diff replaces getTypeSize(CondE->getType())) 
with getIntWidth(CondE->getType())) in ExprEngine::processSwitch.
These calls are not equivalent for bool, see ASTContext.cpp
Add a test case.

Test plan:
make check-clang-analysis
make check-clang

Differential revision: https://reviews.llvm.org/D32328

llvm-svn: 300936