Description:
In 6.1RC2 Writer , it's possible to insert a signature line into a frame. That crashes Writer.


Steps to Reproduce:
1. Create new document in Writer
2. Insert Frame
-> Frame created and chosen
4. Insert Signature Line
-> Window "Signature Line" appears
5. Click OK
->Crash with message box appears:
"LibreOffice 6.1 - Fatal Error: text interface and cursor not related - OK"
(This box only appeared in the Win versions I tested, not in Ubuntu)


Actual Results:
Crash (See steps above)


Expected Results:
IMHO, "Signature Line" should be disabled, as it makes no sense (to me) to insert this into a frame



Reproducible: Always


User Profile Reset: No



Additional Info:
Safe Mode is affected
Win 10, 7 & Ubuntu 18.04 affected
affected with disabled experimental features
Seems that it does not matter, if you vary the options in "Signature Line" window. 

no dublicate found with "frame signature line"

Version: 6.2.0.0.alpha0+
Build ID: 8e9d43546c8e46ea635472ddf07f5c183dc13360
CPU threads: 4; OS: Linux 4.15; UI render: default; VCL: gtk2; 
TinderBox: Linux-rpm_deb-x86_64@70-TDF, Branch:master, Time: 2018-07-12_01:06:03
Locale: en-US (en_US.UTF-8); Calc: group threaded

Version: 6.1.0.2 (x64)
Build ID: b3972dcf1284967612d5ee04fea9d15bcf0cc106
CPU threads: 4; OS: Windows 10.0; UI render: GL; 
Locale: de-DE (de_DE); Calc: group threaded

Version: 6.2.0.0.alpha0+ (x64)
Build ID: 7119184f4b5441600f7b3eae7ec6771c094bbb7f
CPU threads: 4; OS: Windows 6.1; UI render: default; 
TinderBox: Win-x86_64@42, Branch:master, Time: 2018-07-23_05:38:07
Locale: de-DE (de_DE); Calc: group threaded

crashreport.libreoffice.org/stats/crash_details/101ea02e-333f-4504-a0dd-f0aa88f5f637
crashreport.libreoffice.org/stats/crash_details/38d149a8-cfdd-4dba-9a1f-ea842fbd2f64