fix to content file reading error reporting in case of missing dependency

apps/openmw/mwworld/esmstore.cpp

@@ -52,7 +52,7 @@ void ESMStore::load(ESM::ESMReader &esm, Loading::Listener* listener)
         if (index == (int)~0) {
             // Tried to load a parent file that has not been loaded yet. This is bad,
             //  the launcher should have taken care of this.
-            std::string fstring = "File " + fname + " asks for parent file " + masters[j].name
+            std::string fstring = "File " + esm.getName() + " asks for parent file " + masters[j].name
                 + ", but it has not been loaded yet. Please check your load order.";
             esm.fail(fstring);
         }

components/esm/esmreader.cpp

@@ -8,6 +8,11 @@ namespace ESM
 
 using namespace Misc;
 
+    std::string ESMReader::getName() const
+    {
+        return mCtx.filename;
+    }
+
 ESM_Context ESMReader::getContext()
 {
     // Update the file position before returning

components/esm/esmreader.hpp

@@ -38,6 +38,7 @@ public:
   int getFormat() const;
   const NAME &retSubName() const { return mCtx.subName; }
   uint32_t getSubSize() const { return mCtx.leftSub; }
+  std::string getName() const;
 
   /*************************************************************************
    *