[hover] ParseLSPResult sets language 'text' for missing spec (#4699)

I have an LSP that is returning markdown code blocks on Hover with no
language specified, e.g.

````
```
Foobar
```
````

As a result, you get "```" in the message line which is not that useful.

I made the regex to catch the first code fence accept empty language as
well, and if it's empty, we set it to "text".

This makes it so that LSPs that return no language still produce legible
restuls on the message line.

Co-authored-by: Oliver Ruben Albertini <ora@fb.com>

autoload/ale/hover.vim

@@ -117,10 +117,10 @@ function! ale#hover#ParseLSPResult(contents) abort
             for l:line in split(l:item, "\n")
                 if l:fence_language is v:null
                     " Look for the start of a code fence. (```python, etc.)
-                    let l:match = matchlist(l:line, '^``` *\([^ ]\+\) *$')
+                    let l:match = matchlist(l:line, '^``` *\([^ ]\+\)\? *$')
 
                     if !empty(l:match)
-                        let l:fence_language = l:match[1]
+                        let l:fence_language = len(l:match) > 1 ? l:match[1] : 'text'
 
                         if !empty(l:marked_list)
                             call add(l:fence_lines, '')

test/test_hover_parsing.vader

@@ -12,6 +12,22 @@ Execute(Invalid results should be handled):
   AssertEqual [[], []], ale#hover#ParseLSPResult({'kind': 'x', 'value': 'xxx'})
 
 Execute(A string with a code fence should be handled):
+  AssertEqual
+  \ [
+  \   [
+  \   ],
+  \   [
+  \     'def foo():',
+  \     '    pass',
+  \   ],
+  \ ],
+  \ ale#hover#ParseLSPResult(join([
+  \   '```',
+  \   'def foo():',
+  \   '    pass',
+  \   '```',
+  \ ], "\n"))
+
   AssertEqual
   \ [
   \   [