Wrap get_parser in pcall to avoid errors

# Details

Issue: #101

While we still won't be able to parse the file in these error cases it will
at least prevent error messages from being propagated up to the user.

Author: MeanderingProgrammer

Diff for: lua/render-markdown/ui.lua

@@ -115,8 +115,11 @@ end
 ---@param buf integer
 ---@return render.md.Mark[]
 function M.parse_buffer(buf)
+    local has_parser, parser = pcall(vim.treesitter.get_parser, buf)
+    if not has_parser then
+        return {}
+    end
     -- Make sure injections are processed
-    local parser = vim.treesitter.get_parser(buf)
     if not parser:is_valid() then
         parser:parse(true)
     end

Diff for: tests/data/ft_override.md

@@ -0,0 +1,7 @@
+# Mounting sda1
+/dev/sda1 /mnt/shared vfat size=200m
+
+# Mounting tmpfs
+tmpfs /mnt/tmpfs tmpfs size=100m
+
+# vim: ft=fstab

Diff for: tests/ft_override_spec.lua

@@ -0,0 +1,11 @@
+local async_tests = require('plenary.async.tests')
+local util = require('tests.util')
+
+async_tests.describe('ft_override.md', function()
+    async_tests.it('default', function()
+        util.setup('tests/data/ft_override.md')
+
+        local actual = util.get_actual_marks()
+        util.marks_are_equal({}, actual)
+    end)
+end)