Report panic context for SingletonContext.VisitAllModules
Report panic context for SingletonContext.VisitAllModules

If a panic occurs in SingletonContext.VisitAllModules report the
module that was being visited.

Change-Id: Ia7fc07e2e33e9e3c0297903d3b06b7efb33f0105

danw/blueprint,google/blueprint,google/blueprint,danw/blueprint