Bug 470717 - Remove usage of deprecated GetPathFromRegStr macro. r=mcsmurf

suite/installer/windows/nsis/installer.nsi

@@ -346,10 +346,9 @@ Section "-Application" APP_IDX
   ClearErrors
   ReadRegStr $R0 HKLM "Software\Apple Computer, Inc.\QuickTime" "InstallDir"
   ${Unless} ${Errors}
-    Push $R0
-    ${GetPathFromRegStr}
-    Pop $R0
-    ${Unless} ${Errors}
+    ${GetLongPath} $R0 "$R0"
+    ${Unless} $R0 == ""
+      ClearErrors
       GetFullPathName $R0 "$R0\Plugins\nsIQTScriptablePlugin.xpt"
       ${Unless} ${Errors}
         ${LogHeader} "Copying QuickTime Scriptable Component"