tdf#118219 sw: fix SwCursorShell::GetContentAtPos() redline crash

The problem is that CalcStartEnd() will not return the length of the
node, but COMPLETE_STRING if the redline ends in a subsequent node.

(regression from 4966b1d4)

Change-Id: Ic0a27f87b79f68417777842c611c2129fdc9b1f9
Reviewed-on: https://gerrit.libreoffice.org/56402
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>

sw/source/core/crsr/crstrvl.cxx

@@ -1556,6 +1556,17 @@ bool SwCursorShell::GetContentAtPos( const Point& rPt,
                             sal_Int32 nStart;
                             sal_Int32 nEnd;
                             pRedl->CalcStartEnd(pTextNd->GetIndex(), nStart, nEnd);
+                            if (nStart == COMPLETE_STRING)
+                            {
+                                // consistency: found pRedl, so there must be
+                                // something in pTextNd
+                                assert(nEnd != COMPLETE_STRING);
+                                nStart = 0;
+                            }
+                            if (nEnd == COMPLETE_STRING)
+                            {
+                                nEnd = pTextNd->Len();
+                            }
                             //get bounding box of range
                             SwRect aStart;
                             pFrame->GetCharRect(aStart, SwPosition(*pTextNd, nStart), &aTmpState);