Simplify a bit buffer iteration functions

Dont try to ensure the returned value is valid, incrementing past
the end/decrementing before begin is the caller's error.

src/buffer.cc

@@ -639,36 +639,23 @@ BufferCoord Buffer::char_next(BufferCoord coord) const
     if (coord.column < m_lines[coord.line].length() - 1)
     {
         auto line = m_lines[coord.line];
-        coord.column += utf8::codepoint_size(line[coord.column]);
+        auto column = coord.column + utf8::codepoint_size(line[coord.column]);
-        // Handle invalid utf-8
+        if (column >= line.length()) // Handle invalid utf-8
-        if (coord.column >= line.length())
+            return { coord.line + 1, 0 };
-        {
+        return { coord.line, column };
-            ++coord.line;
-            coord.column = 0;
     }
-    }
+    return { coord.line + 1, 0 };
-    else
-    {
-        ++coord.line;
-        coord.column = 0;
-    }
-    return coord;
 }
 
 BufferCoord Buffer::char_prev(BufferCoord coord) const
 {
     kak_assert(is_valid(coord));
     if (coord.column == 0)
-    {
+        return { coord.line - 1, m_lines[coord.line - 1].length() - 1 };
-        if (coord.line > 0)
+
-            coord.column = m_lines[--coord.line].length() - 1;
-    }
-    else
-    {
     auto line = m_lines[coord.line];
-        coord.column = (int)(utf8::character_start(line.begin() + (int)coord.column - 1, line.begin()) - line.begin());
+    auto column = (int)(utf8::character_start(line.begin() + (int)coord.column - 1, line.begin()) - line.begin());
-    }
+    return { coord.line, column };
-    return coord;
 }
 
 timespec Buffer::fs_timestamp() const

src/buffer.inl.hh

@@ -16,25 +16,15 @@ inline const char& Buffer::byte_at(BufferCoord c) const
 inline BufferCoord Buffer::next(BufferCoord coord) const
 {
     if (coord.column < m_lines[coord.line].length() - 1)
-        ++coord.column;
+        return {coord.line, coord.column + 1};
-    else
+    return { coord.line + 1, 0 };
-    {
-        ++coord.line;
-        coord.column = 0;
-    }
-    return coord;
 }
 
 inline BufferCoord Buffer::prev(BufferCoord coord) const
 {
     if (coord.column == 0)
-    {
+        return { coord.line - 1, m_lines[coord.line - 1].length() - 1 };
-        if (coord.line > 0)
+    return { coord.line, coord.column - 1 };
-            coord.column = m_lines[--coord.line].length() - 1;
-    }
-    else
-       --coord.column;
-    return coord;
 }
 
 inline ByteCount Buffer::distance(BufferCoord begin, BufferCoord end) const
@@ -53,11 +43,9 @@ inline ByteCount Buffer::distance(BufferCoord begin, BufferCoord end) const
 
 inline bool Buffer::is_valid(BufferCoord c) const
 {
-    if (c.line < 0 or c.column < 0)
+    return (c.line >= 0 and c.column >= 0) and
-        return false;
+           ((c.line < line_count() and c.column < m_lines[c.line].length()) or
-
+            (c.line == line_count() and c.column == 0));
-    return (c.line < line_count() and c.column < m_lines[c.line].length()) or
-           (c.line == line_count() and c.column == 0);
 }
 
 inline bool Buffer::is_end(BufferCoord c) const
@@ -67,7 +55,7 @@ inline bool Buffer::is_end(BufferCoord c) const
 
 inline BufferIterator Buffer::begin() const
 {
-    return {*this, { 0_line, 0 }};
+    return {*this, { 0, 0 }};
 }
 
 inline BufferIterator Buffer::end() const
@@ -78,7 +66,7 @@ inline BufferIterator Buffer::end() const
 [[gnu::always_inline]]
 inline LineCount Buffer::line_count() const
 {
-    return LineCount(m_lines.size());
+    return LineCount{(int)m_lines.size()};
 }
 
 inline size_t Buffer::timestamp() const