out-of-bounds access on Enter-up-left in new text field

Reproduce using:
1. Select text tool (F8)
2. Click on empty canvas
3. Hit Enter
4. Hit Up
5. Hit Left

Backport from 1.0alpha master
Cherry picked from 60e14d32

src/libnrtype/Layout-TNG-OutIter.cpp

@@ -502,7 +502,7 @@ void Layout::queryCursorShape(iterator const &it, Geom::Point &position, double
                 if (it._glyph_index == -1) {
                     rotation = 0.0;
                 } else if(it._glyph_index == 0) {
-                    rotation = _glyphs[0].rotation;
+                    rotation = _glyphs.empty() ? 0.0 : _glyphs[0].rotation;
                 } else{
                     rotation = _glyphs[it._glyph_index - 1].rotation;
                 }