patch 8.1.0181: memory leak with trailing characters in skip expression

Problem:    Memory leak with trailing characters in skip expression.
Solution:   Free the return value.

src/eval.c

@@ -729,6 +729,7 @@ eval_expr_typval(typval_T *expr, typval_T *argv, int argc, typval_T *rettv)
 	    return FAIL;
 	if (*s != NUL)  /* check for trailing chars after expr */
 	{
+	    clear_tv(rettv);
 	    EMSG2(_(e_invexpr2), s);
 	    return FAIL;
 	}

src/testdir/test_search.vim

@@ -324,6 +324,16 @@ func Test_searchpair_skip()
     bw!
 endfunc
 
+func Test_searchpair_leak()
+  new
+  call setline(1, 'if one else another endif')
+
+  " The error in the skip expression caused memory to leak.
+  call assert_fails("call searchpair('\\<if\\>', '\\<else\\>', '\\<endif\\>', '', '\"foo\" 2')", 'E15:')
+
+  bwipe!
+endfunc
+
 func Test_searchc()
   " These commands used to cause memory overflow in searchc().
   new

src/version.c

@@ -789,6 +789,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    181,
 /**/
     180,
 /**/