Fix: (link) Don't match against null groups

e.g. in a source block containing Bash shell code like:

  [[ -z $data ]]

The matched groups could be null, since it's not actually an Org link,
so calling STRING-MATCH-P on them would signal an error.

Reported-by: John Wiegley <jwiegley@gmail.com>

README.org

@@ -555,7 +555,8 @@ Simple links may also be written manually in either sexp or non-sexp form, like:
 
 ** 0.8.10-pre
 
-Nothing new yet.
+*Fixes*
++ Predicate ~link~ could signal an error when searching text that is mistakenly recognized as an Org link (e.g. Bash double-bracket constructs in a source block).  (Thanks to [[https://github.com/jwiegley][John Wiegley]] for reporting.)
 
 ** 0.8.9
 

org-ql.el

@@ -1626,11 +1626,15 @@ any link is found."
                          (or (null description)
                              (string-match-p description (match-string org-ql-link-description-group)))))
               (_ (if (and description target)
-                     (and (string-match-p target (match-string 1))
-                          (string-match-p description (match-string org-ql-link-description-group)))
-                   (or (string-match-p description-or-target (match-string 1))
+                     (and (and (match-string 1)
+                               (string-match-p target (match-string 1)))
+                          (and (match-string org-ql-link-description-group)
+                               (string-match-p description (match-string org-ql-link-description-group))))
+                   (or (and (match-string 1)
+                            (string-match-p description-or-target (match-string 1)))
+                       (and (match-string org-ql-link-description-group)
                             (string-match-p description-or-target
-                                       (match-string org-ql-link-description-group)))))))))
+                                            (match-string org-ql-link-description-group))))))))))
 
 (org-ql-defpred (rifle smart) (&rest strings)
   "Return non-nil if each of strings is found in the entry or its outline path.

org-ql.info

@@ -1086,7 +1086,11 @@ File: README.info,  Node: 0810-pre,  Next: 089,  Up: Changelog
 5.1 0.8.10-pre
 ==============
 
-Nothing new yet.
+*Fixes*
+   • Predicate ‘link’ could signal an error when searching text that is
+     mistakenly recognized as an Org link (e.g.  Bash double-bracket
+     constructs in a source block).  (Thanks to John Wiegley
+     (https://github.com/jwiegley) for reporting.)
 
 
 File: README.info,  Node: 089,  Next: 088,  Prev: 0810-pre,  Up: Changelog
@@ -2093,50 +2097,50 @@ Node: Links38955
 Node: Tips39642
 Node: Changelog39966
 Node: 0810-pre40932
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-Node: 0177578
-Node: Notes77679
-Node: Comparison with Org Agenda searches77841
-Node: org-sidebar78730
-Node: License79009
+Node: 08941297
+Node: 08842441
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+Node: Comparison with Org Agenda searches78091
+Node: org-sidebar78980
+Node: License79259
 
 End Tag Table