ox-latex: Fix items starting with a square bracket

* lisp/ox-latex.el (org-latex-headline, org-latex-item): Fix items
  starting with a square bracket.

Thanks to Jon Degenhardt, Vladimir Lomov and Eric S Fraga for
contributing to the discussion.

lisp/ox-latex.el

@@ -1374,7 +1374,13 @@ holding contextual information."
 		  (when (org-export-first-sibling-p headline info)
 		    (format "\\begin{%s}\n" (if numberedp 'enumerate 'itemize)))
 		  ;; Itemize headline
-		  "\\item " full-text "\n" headline-label pre-blanks contents)))
+		  "\\item"
+		  (and full-text (org-string-match-p "\\`[ \t]*\\[" full-text)
+		       "\\relax")
+		  " " full-text "\n"
+		  headline-label
+		  pre-blanks
+		  contents)))
 	    ;; If headline is not the last sibling simply return
 	    ;; LOW-LEVEL-BODY.  Otherwise, also close the list, before
 	    ;; any blank line.
@@ -1564,7 +1570,25 @@ contextual information."
 		(and tag (format "[{%s}] "
 				 (concat checkbox
 					 (org-export-data tag info)))))))
-    (concat counter "\\item" (or tag (concat " " checkbox))
+    (concat counter
+	    "\\item"
+	    (cond
+	     (tag)
+	     (checkbox (concat " " checkbox))
+	     ;; Without a tag or a check-box, if CONTENTS starts with
+	     ;; an opening square bracket, add "\relax" to "\item",
+	     ;; unless the brackets comes from an initial export
+	     ;; snippet (i.e. it is inserted willingly by the user).
+	     ((and contents
+		   (org-string-match-p "\\`[ \t]*\\[" contents)
+		   (not (let ((e (car (org-element-contents item))))
+			  (and (eq (org-element-type e) 'paragraph)
+			       (let ((o (car (org-element-contents e))))
+				 (and (eq (org-element-type o) 'export-snippet)
+				      (eq (org-export-snippet-backend o)
+					  'latex)))))))
+	      "\\relax ")
+	     (t " "))
 	    (and contents (org-trim contents))
 	    ;; If there are footnotes references in tag, be sure to
 	    ;; add their definition at the end of the item.  This