[Fix clojure-emacs#593] clojure-find-ns breaks if the ns form is preceded by ws

Problem was that the regexp here expected (ns form to start right in the
beginning of the line. I added zero or more whitespace in the beginning which
corrects the issue.

Adds also a unit test which covers the issue.

Author: jogo3000

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## master (unreleased)
 
+### Bugs fixed
+* [#593] clojure-find-ns breaks if the ns form is preceded by whitespace
+
 ## 5.13.0 (2021-05-05)
 
 ### New features

clojure-mode.el

@@ -1873,7 +1873,7 @@ content) are considered part of the preceding sexp."
 (make-obsolete-variable 'clojure-namespace-name-regex 'clojure-namespace-regexp "5.12.0")
 
 (defconst clojure-namespace-regexp
-  (rx line-start "(" (? "clojure.core/") (or "in-ns" "ns" "ns+") symbol-end))
+  (rx line-start (zero-or-more whitespace) "(" (? "clojure.core/") (or "in-ns" "ns" "ns+") symbol-end))
 
 (defcustom clojure-cache-ns nil
   "Whether to cache the results of `clojure-find-ns'.

test/clojure-mode-util-test.el

@@ -61,6 +61,8 @@
   (it "should find common namespace declarations"
     (with-clojure-buffer "(ns foo)"
       (expect (clojure-find-ns) :to-equal "foo"))
+    (with-clojure-buffer " (ns foo)"
+      (expect (clojure-find-ns) :to-equal "foo"))
     (with-clojure-buffer "(ns
     foo)"
       (expect (clojure-find-ns) :to-equal "foo"))