purescript-indentation.el: don't modify buffer if indentation unchanged

Currently calling indentation on a line that is already indented as
expected results in buffer being modified despite no changes being
actually done. Avoid this by checking if current indentation already
matches the one we just calculated and only reindenting on mismatch.

purescript-indentation.el

@@ -196,17 +196,18 @@ autofill-mode."
       (end-of-line))))
 
 (defun purescript-indentation-reindent (col)
-  (beginning-of-line)
-  (delete-region (point)
-                 (progn
-                   (when (and (eq purescript-literate 'bird)
-                              (eq (char-after) ?>))
-                     (forward-char))
-                   (skip-syntax-forward "-")
-                   (point)))
-  (when (eq purescript-literate 'bird)
-    (insert ">"))
-  (indent-to col))
+  (unless (= col (purescript-indentation-current-indentation))
+    (beginning-of-line)
+    (delete-region (point)
+                   (progn
+                     (when (and (eq purescript-literate 'bird)
+                                (eq (char-after) ?>))
+                       (forward-char))
+                     (skip-syntax-forward "-")
+                     (point)))
+    (when (eq purescript-literate 'bird)
+      (insert ">"))
+    (indent-to col)))
 
 (defun purescript-indentation-current-indentation ()
   (if (eq purescript-literate 'bird)