patch 8.0.0254: error message of assert functions is sometimes incomplete

Problem:    When using an assert function one can either specify a message or
            get a message about what failed, not both.
Solution:   Concatenate the error with the message.
diff --git a/src/eval.c b/src/eval.c
index 5846936..a5ae4f8 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -9240,35 +9240,34 @@
 
     if (opt_msg_tv->v_type != VAR_UNKNOWN)
     {
-	ga_concat(gap, tv2string(opt_msg_tv, &tofree, numbuf, 0));
+	ga_concat(gap, echo_string(opt_msg_tv, &tofree, numbuf, 0));
+	vim_free(tofree);
+	ga_concat(gap, (char_u *)": ");
+    }
+
+    if (atype == ASSERT_MATCH || atype == ASSERT_NOTMATCH)
+	ga_concat(gap, (char_u *)"Pattern ");
+    else if (atype == ASSERT_NOTEQUAL)
+	ga_concat(gap, (char_u *)"Expected not equal to ");
+    else
+	ga_concat(gap, (char_u *)"Expected ");
+    if (exp_str == NULL)
+    {
+	ga_concat_esc(gap, tv2string(exp_tv, &tofree, numbuf, 0));
 	vim_free(tofree);
     }
     else
+	ga_concat_esc(gap, exp_str);
+    if (atype != ASSERT_NOTEQUAL)
     {
-	if (atype == ASSERT_MATCH || atype == ASSERT_NOTMATCH)
-	    ga_concat(gap, (char_u *)"Pattern ");
-	else if (atype == ASSERT_NOTEQUAL)
-	    ga_concat(gap, (char_u *)"Expected not equal to ");
+	if (atype == ASSERT_MATCH)
+	    ga_concat(gap, (char_u *)" does not match ");
+	else if (atype == ASSERT_NOTMATCH)
+	    ga_concat(gap, (char_u *)" does match ");
 	else
-	    ga_concat(gap, (char_u *)"Expected ");
-	if (exp_str == NULL)
-	{
-	    ga_concat_esc(gap, tv2string(exp_tv, &tofree, numbuf, 0));
-	    vim_free(tofree);
-	}
-	else
-	    ga_concat_esc(gap, exp_str);
-	if (atype != ASSERT_NOTEQUAL)
-	{
-	    if (atype == ASSERT_MATCH)
-		ga_concat(gap, (char_u *)" does not match ");
-	    else if (atype == ASSERT_NOTMATCH)
-		ga_concat(gap, (char_u *)" does match ");
-	    else
-		ga_concat(gap, (char_u *)" but got ");
-	    ga_concat_esc(gap, tv2string(got_tv, &tofree, numbuf, 0));
-	    vim_free(tofree);
-	}
+	    ga_concat(gap, (char_u *)" but got ");
+	ga_concat_esc(gap, tv2string(got_tv, &tofree, numbuf, 0));
+	vim_free(tofree);
     }
 }