[clang] [clang] fix divide by zero in ComplexExprEvaluator (PR #104666)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

For future reference the summary here is not really sufficient. Since this what usually goes in the git log they should be enough details for folks reading the git log to understand what the change was.

The summary should explain the problem and provide a summary of the fix as well.

https://github.com/llvm/llvm-project/pull/104666