Add checking versions of iterator movement functions

src/core/GapBuffer.cc

@@ -40,6 +40,21 @@ void GapBuffer::Iterator::forward()
     }
 }
 
+bool GapBuffer::Iterator::check_forward()
+{
+    if (valid())
+    {
+        Iterator i2 = *this;
+        i2.forward();
+        if (i2.valid())
+        {
+            m_offset = i2.m_offset;
+            return true;
+        }
+    }
+    return false;
+}
+
 void GapBuffer::Iterator::back()
 {
     if (valid())
@@ -56,3 +71,18 @@ void GapBuffer::Iterator::back()
         }
     }
 }
+
+bool GapBuffer::Iterator::check_back()
+{
+    if (valid())
+    {
+        Iterator i2 = *this;
+        i2.back();
+        if (i2.valid())
+        {
+            m_offset = i2.m_offset;
+            return true;
+        }
+    }
+    return false;
+}

src/core/GapBuffer.h

@@ -23,7 +23,9 @@ public:
             return m_offset < m_gap_buffer->size();
         }
         void forward();
+        bool check_forward();
         void back();
+        bool check_back();
         uint8_t * address() const
         {
             return m_gap_buffer->address(m_offset);