stringapi: Use strings for TryFullPath

Source/cmSourceFile.cxx

@@ -164,7 +164,7 @@ bool cmSourceFile::FindFullPath(std::string* error)
       }
     tryPath += this->Location.GetName();
     tryPath = cmSystemTools::CollapseFullPath(tryPath.c_str(), *di);
-    if(this->TryFullPath(tryPath.c_str(), 0))
+    if(this->TryFullPath(tryPath.c_str(), ""))
       {
       return true;
       }
@@ -217,10 +217,11 @@ bool cmSourceFile::FindFullPath(std::string* error)
 }
 
 //----------------------------------------------------------------------------
-bool cmSourceFile::TryFullPath(const char* tp, const char* ext)
+bool cmSourceFile::TryFullPath(const std::string& path,
+                               const std::string& ext)
 {
-  std::string tryPath = tp;
-  if(ext && *ext)
+  std::string tryPath = path;
+  if(!ext.empty())
     {
     tryPath += ".";
     tryPath += ext;

Source/cmSourceFile.h

@@ -107,7 +107,7 @@ private:
   bool FindFullPathFailed;
 
   bool FindFullPath(std::string* error);
-  bool TryFullPath(const char* tryPath, const char* ext);
+  bool TryFullPath(const std::string& path, const std::string& ext);
   void CheckExtension();
   void CheckLanguage(std::string const& ext);