Fix handling of empty strings in NIF string tables

apps/openmw_test_suite/nifloader/testbulletnifloader.cpp

@@ -266,7 +266,7 @@ namespace
         MOCK_CONST_METHOD0(numRecords, std::size_t ());
         MOCK_CONST_METHOD1(getRoot, Nif::Record* (std::size_t));
         MOCK_CONST_METHOD0(numRoots, std::size_t ());
-        MOCK_CONST_METHOD1(getString, std::string (std::size_t));
+        MOCK_CONST_METHOD1(getString, std::string (uint32_t));
         MOCK_METHOD1(setUseSkinning, void (bool));
         MOCK_CONST_METHOD0(getUseSkinning, bool ());
         MOCK_CONST_METHOD0(getFilename, std::string ());

components/nif/niffile.hpp

@@ -26,7 +26,7 @@ struct File
 
     virtual size_t numRoots() const = 0;
 
-    virtual std::string getString(size_t index) const = 0;
+    virtual std::string getString(uint32_t index) const = 0;
 
     virtual void setUseSkinning(bool skinning) = 0;
 
@@ -129,8 +129,10 @@ public:
     size_t numRoots() const override { return roots.size(); }
 
     /// Get a given string from the file's string table
-    std::string getString(size_t index) const override
+    std::string getString(uint32_t index) const override
     {
+        if (index == std::numeric_limits<uint32_t>::max())
+            return std::string();
         return strings.at(index);
     }