Ide: sentences found by find_phrase_starting_at should be nonempty (fix #2683)
Ide: sentences found by find_phrase_starting_at should be nonempty (fix #2683)

 In addition to #2683, this also prevent Vernac.End_of_input
 exceptions when a buffer ends with one of the new delimiters -+*{}.

git-svn-id: 44dc50bdcc0f5d1a212c497508dc9452e0b35e2b@14989 85f007b7-540e-0410-9357-904b9bb8a0f7

jhjourdan/coq,pirapira/coq2rust,herbelin/github-coq,shindere/coq,ejgallego/coq,8l/coq,silene/coq,gares/coq,ejgallego/coq,Lionel-Rieg/coq,ejgallego/coq,coq/coq,TOSPIO/coq,ppedrot/coq,letouzey/coq-wip,barras/coq,ale-f/coq,herbelin/github-coq,coq/coq,shindere/coq,asr/coq,jpdeplaix/coq,pirbo/coq,Lionel-Rieg/coq,maximedenes/coq,jpdeplaix/coq,pirapira/coq2rust,barras/coq,maximedenes/coq,shindere/coq,ppedrot/coq,jhjourdan/coq,maximedenes/coq,coq/coq,aspiwack/coq,gmalecha/coq,william-lawvere/coq,amintimany/coq,Ptival/coq,gmalecha/coq,Matafou/coq,Matafou/coq,mattam82/coq,Zimmi48/coq,Zimmi48/coq,barras/coq,JasonGross/coq,Ptival/coq,jhjourdan/coq,mlasson/coq,Matafou/coq,gares/coq,SkySkimmer/coq,mlasson/coq,gares/coq,william-lawvere/coq,TheTypoMaster/coq,silene/coq,letouzey/coq-wip,gmalecha/coq,TOSPIO/coq,Ptival/coq,asr/coq,TheTypoMaster/coq,gares/coq,ejgallego/coq,mlasson/coq,Zimmi48/coq,amintimany/coq,JasonGross/coq,aspiwack/coq,JasonGross/coq,maximedenes/coq,ppedrot/coq,letouzey/coq-wip,jpdeplaix/coq,SkySkimmer/coq,gares/coq,TheTypoMaster/coq,amintimany/coq,SkySkimmer/coq,silene/coq,ale-f/coq,pirbo/coq,JasonGross/coq,letouzey/coq-wip,ale-f/coq,Zimmi48/coq,TOSPIO/coq,herbelin/github-coq,ppedrot/coq,pirapira/coq2rust,letouzey/coq-wip,coq/coq,william-lawvere/coq,8l/coq,ppedrot/coq,pirbo/coq,maximedenes/coq,asr/coq,aspiwack/coq,8l/coq,mattam82/coq,SkySkimmer/coq,mattam82/coq,Lionel-Rieg/coq