Make sure the record hasn't ended in getHString hack (bug #4938)

CHANGELOG.md

@@ -48,6 +48,7 @@
     Bug #4911: Editor: QOpenGLContext::swapBuffers() warning with Qt5
     Bug #4916: Specular power (shininess) material parameter is ignored when shaders are used.
     Bug #4922: Werewolves can not attack if the transformation happens during attack
+    Bug #4938: Strings from subrecords with actually empty headers can't be empty
     Feature #2229: Improve pathfinding AI
     Feature #3442: Default values for fallbacks from ini file
     Feature #3610: Option to invert X axis

components/esm/esmreader.cpp

@@ -127,7 +127,7 @@ std::string ESMReader::getHString()
     // them. For some reason, they break the rules, and contain a byte
     // (value 0) even if the header says there is no data. If
     // Morrowind accepts it, so should we.
-    if (mCtx.leftSub == 0)
+    if (mCtx.leftSub == 0 && mCtx.leftRec != 0)
     {
         // Skip the following zero byte
         mCtx.leftRec--;