lsp: Handle end lines in apply_text_edits (#12314)

If the LSP sends an end line that is larger than what nvim considers to be the
last line, you get an Index out of bounds error when fetching the line from
nvim, a change that was introduced in #12223. This change removes the strict
indexing and checks the return value from nvim_buf_get_lines.

runtime/lua/vim/lsp/util.lua

@@ -94,6 +94,19 @@ local edit_sort_key = sort_by_key(function(e)
   return {e.A[1], e.A[2], e.i}
 end)
 
+local function get_line_byte_from_line_character(bufnr, lnum, cnum)
+  -- Skip check when the byte and character position is the same
+  if cnum > 0 then
+    local lines = api.nvim_buf_get_lines(bufnr, lnum, lnum+1, false)
+
+    if #lines > 0 then
+      return vim.str_byteindex(lines[1], cnum)
+    end
+  end
+
+  return cnum
+end
+
 function M.apply_text_edits(text_edits, bufnr)
   if not next(text_edits) then return end
   if not api.nvim_buf_is_loaded(bufnr) then
@@ -104,13 +117,15 @@ function M.apply_text_edits(text_edits, bufnr)
   for i, e in ipairs(text_edits) do
     -- adjust start and end column for UTF-16 encoding of non-ASCII characters
     local start_row = e.range.start.line
-    local start_col = e.range.start.character
-    local start_bline = api.nvim_buf_get_lines(bufnr, start_row, start_row+1, true)[1]
-    start_col = vim.str_byteindex(start_bline, start_col)
+    local start_col = get_line_byte_from_line_character(
+      bufnr,
+      start_row,
+      e.range.start.character)
     local end_row = e.range["end"].line
-    local end_col = e.range["end"].character
-    local end_bline = api.nvim_buf_get_lines(bufnr, end_row, end_row+1, true)[1]
-    end_col = vim.str_byteindex(end_bline, end_col)
+    local end_col = get_line_byte_from_line_character(
+      bufnr,
+      end_row,
+      e.range["end"].character)
     start_line = math.min(e.range.start.line, start_line)
     finish_line = math.max(e.range["end"].line, finish_line)
     -- TODO(ashkan) sanity check ranges for overlap.