If a file is saved as, reset its master if it has any, thus preventing a crash (bug 8161)

src/Buffer.cpp

@@ -4591,6 +4591,7 @@ bool Buffer::saveAs(FileName const & fn)
 		// we need to check that the locations of child buffers
 		// are still valid.
 		checkChildBuffers();
+		checkMasterBuffer();
 		return true;
 	} else {
 		// save failed
@@ -4639,4 +4640,25 @@ void Buffer::checkChildBuffers()
 	d->position_to_children.clear();
 }
 
+
+// If a child has been saved under a different name/path, it might have been
+// orphaned. Therefore the master needs to be reset (bug 8161).
+void Buffer::checkMasterBuffer()
+{
+	Buffer const * const master = masterBuffer();
+	if (master == this)
+		return;
+
+	// necessary to re-register the child (bug 5873)
+	// FIXME: clean up updateMacros (here, only
+	// child registering is needed).
+	master->updateMacros();
+	// (re)set master as master buffer, but only
+	// if we are a real child
+	if (master->isChild(this))
+		setParent(master);
+	else
+		setParent(0);
+}
+
 } // namespace lyx

src/Buffer.h

@@ -691,6 +691,8 @@ public:
 		WordLangTuple & word_lang, docstring_list & suggestions) const;
 	///
 	void checkChildBuffers();
+	///
+	void checkMasterBuffer();
 
 	/// compute statistics between \p from and \p to
 	/// \p from initial position