[NFCI] Always initialize BugReport const fields

[xiaobai]

Summary

Some compilers require that const fields of an object must be explicitly
initialized by the constructor. I ran into this issue building with clang
3.8 on Ubuntu 16.04.

[Szelethus]

LGTM, thanks!

cfe/trunk/include/clang/StaticAnalyzer/Core/BugReporter/BugReporter.h

public:
 
   /// Create a BugReport with a custom uniqueing location.
   ///
   /// The reports that have the same report location, description, bug type, and
   /// ranges are uniqued - only one of the equivalent reports will be presented
   /// to the user. This method allows to rest the location which should be used
   /// for uniquing reports. For example, memory leaks checker, could set this to
   /// the allocation site, rather then the location where the bug is reported.
-  BugReport(BugType& bt, StringRef desc, const ExplodedNode *errornode,
+  BugReport(BugType &bt, StringRef desc, const ExplodedNode *errornode,
             PathDiagnosticLocation LocationToUnique, const Decl *DeclToUnique)
       : BT(bt), Description(desc), UniqueingLocation(LocationToUnique),
-        UniqueingDecl(DeclToUnique), ErrorNode(errornode) {}
+        UniqueingDecl(DeclToUnique), ErrorNode(errornode),
+        ErrorNodeRange(getStmt() ? getStmt()->getSourceRange()
+                                 : SourceRange()) {}
 
   virtual ~BugReport() = default;
 
   const BugType& getBugType() const { return BT; }
   //BugType& getBugType() { return BT; }
 
   /// True when the report has an execution path associated with it.
   ///