distancefieldgenerator: Fix failure reading CMAP for some fonts

If all the range offsets in the type 4 subtable in CMAP
is equal to 0, there is no need for a glyph ID array, so
this array can actually have zero length.

We did not account for this, and would fail to read those
fonts.

Task-number: QTBUG-76188
Change-Id: I11873fba7214d179af1fcd7ccff9a9fd1c72ce10
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/distancefieldgenerator/distancefieldmodelworker.cpp

@@ -148,7 +148,7 @@ void DistanceFieldModelWorker::readCmapSubtable(const CmapSubtable4 *subtable, c
     const qint16 *idDeltas = reinterpret_cast<const qint16 *>(startCodes + segCount);
     const quint16 *idRangeOffsets = reinterpret_cast<const quint16 *>(idDeltas + segCount);
     const quint16 *glyphIdArray = idRangeOffsets + segCount;
-    if (glyphIdArray >= end) {
+    if (glyphIdArray > end) {
         emit error(tr("End of cmap table reached when parsing subtable format '4'"));
         return;
     }