[LyX/master] Fix bug #9907: We get a crash if we first close a master buffer one of whose children is also a child of another buffer, then try to close that one.

[Richard Heck]

commit 0407364392abca866ee5a3da3c89ad41811ed81f
Author: Richard Heck <rgh...@lyx.org>
Date:   Tue Jan 5 09:53:42 2016 -0500

    Fix bug #9907: We get a crash if we first close a master buffer one of
    whose children is also a child of another buffer, then try to close that
    one.
    
    The problem is that we do not check properly to make sure that the child
    is not a child of some other buffer. Now we do.

diff --git a/src/frontends/qt4/GuiView.cpp b/src/frontends/qt4/GuiView.cpp
index 548381b..c2101f3 100644
--- a/src/frontends/qt4/GuiView.cpp
+++ b/src/frontends/qt4/GuiView.cpp
@@ -2849,23 +2849,31 @@ bool GuiView::closeBuffer(Buffer & buf)
                ListOfBuffers::const_iterator it = clist.begin();
                ListOfBuffers::const_iterator const bend = clist.end();
                for (; it != bend; ++it) {
-                       // If a child is dirty, do not close
-                       // without user intervention
-                       //FIXME: should we look in other tabworkareas?
                        Buffer * child_buf = *it;
+                       if (theBufferList().isOthersChild(&buf, child_buf)) {
+                               child_buf->setParent(0);
+                               continue;
+                       }
+
+                       // FIXME: should we look in other tabworkareas?
+                       // ANSWER: I don't think so. I've tested, and if the 
child is
+                       // open in some other window, it closes without a 
problem.
                        GuiWorkArea * child_wa = workArea(*child_buf);
                        if (child_wa) {
-                               if (!closeWorkArea(child_wa, true)) {
-                                       success = false;
+                               success = closeWorkArea(child_wa, true);
+                               if (!success)
                                        break;
-                               }
-                       } else
-                               theBufferList().releaseChild(&buf, child_buf);
+                       } else {
+                               // In this case the child buffer is open but 
hidden.
+                               // It therefore should not (MUST NOT) be dirty!
+                               LATTEST(child_buf->isClean());
+                               theBufferList().release(child_buf);
+                       }
                }
        }
        if (success) {
                // goto bookmark to update bookmark pit.
-               //FIXME: we should update only the bookmarks related to this 
buffer!
+               // FIXME: we should update only the bookmarks related to this 
buffer!
                LYXERR(Debug::DEBUG, "GuiView::closeBuffer()");
                for (size_t i = 0; i < theSession().bookmarks().size(); ++i)
                        guiApp->gotoBookmark(i+1, false, false);