DisplayBuffer: overload atom_containing with a version taking an iterator to search start

src/display_buffer.cc

@@ -88,10 +88,16 @@ DisplayBuffer::iterator DisplayBuffer::insert(iterator where, const DisplayAtom&
 
 DisplayBuffer::iterator DisplayBuffer::atom_containing(const BufferIterator& where)
 {
-    for (iterator it = m_atoms.begin(); it != m_atoms.end(); ++it)
+    return atom_containing(where, m_atoms.begin());
+}
+
+DisplayBuffer::iterator DisplayBuffer::atom_containing(const BufferIterator& where,
+                                                       iterator start)
+{
+    for (iterator it = start; it != m_atoms.end(); ++it)
     {
         if (it->end() > where)
-            return it;
+            return it->begin() <= where ? it : end();
     }
     return end();
 }

src/display_buffer.hh

@@ -113,6 +113,7 @@ public:
     const_iterator end()   const { return m_atoms.end(); }
 
     iterator atom_containing(const BufferIterator& where);
+    iterator atom_containing(const BufferIterator& where, iterator start);
 
     const DisplayAtom& front() const { return m_atoms.front(); }
     const DisplayAtom& back()  const { return m_atoms.back(); }