fix(parser): Added parser check to prevent crashes on nvim-0.12

Based on the commit from ZX.

Closes: #492, #488
Co-author: zhengxin5 <zx19880528@gmail.com>

Author: OXY2DEV

lua/markview/parser.lua

@@ -150,14 +150,15 @@ parser.init = function (buffer, from, to, cache)
 		return parser.content, parser.sorted;
 	end
 
-    vim.treesitter.get_parser(buffer):parse(true);
 	local root_parser = vim.treesitter.get_parser(buffer);
 
 	if not root_parser then
 		-- Can't find root parser.
 		return parser.content, parser.sorted;
 	end
 
+	root_parser:parse(true);
+
 	--[[
 		WARN: Recursion when parsing `asciidoc_inline` trees
 
@@ -249,14 +250,15 @@ parser.parse_links = function (buffer)
 		return;
 	end
 
-    vim.treesitter.get_parser(buffer):parse(true);
 	local root_parser = vim.treesitter.get_parser(buffer);
 
 	if not root_parser then
 		-- Can't find root parser.
 		return parser.content, parser.sorted;
 	end
 
+	root_parser:parse(true);
+
 	---|fS "chore: Announce start of parsing"
 	---@type integer Start time
 	local start = vim.uv.hrtime();

lua/markview/spec.lua

@@ -201,9 +201,7 @@ spec.default = {
 			end
 
 			local success, parser = pcall(vim.treesitter.get_parser, buffer);
-			if success and parser ~= nil then
-				return true;
-			end
+			return success and parser ~= nil;
 		end,
 
 		raw_previews = {},