[flang] Fix `LoweringBridge::validModule`

[awarzynski]

Summary

This patch updates validModule not to use getModule. getModule
will dereference module, but that will lead to a seg-fault if module
is a nullptr.

[schweitz]

flang/include/flang/Lower/Bridge.h

87

Someone else called this "Yoda style". But their question remains: why use it?

[awarzynski]

flang/include/flang/Lower/Bridge.h

87

Yoda Condition ;-)

Tl:Dr With this style, you will never write var = 0 instead of var == 0 (compilers will complain about 0 = var, but not about 0 == var). Happy to change to module != nullptr if that's what you prefer.

[schweitz]

flang/include/flang/Lower/Bridge.h

87

I expect that module != nullptr wouldn't attract any attention. ;)

[awarzynski]

Swap the comparison

flang/include/flang/Lower/Bridge.h

public:
   }
 
   /// Get the kind map.
   const fir::KindMapping &getKindMap() const { return kindMap; }
 
   /// Create a folding context. Careful: this is very expensive.
   Fortran::evaluate::FoldingContext createFoldingContext() const;
 
-  bool validModule() { return getModule(); }
+  bool validModule() { return (module != nullptr); }
 
   //===--------------------------------------------------------------------===//
   // Perform the creation of an mlir::ModuleOp
   //===--------------------------------------------------------------------===//
 
   /// Read in an MLIR input file rather than lowering Fortran sources.
   /// This is intended to be used for testing.
   void parseSourceFile(llvm::SourceMgr &);