Point out missing if conditional

On a case where an else conditional is missing, point this out
instead of the token immediately after the (incorrect) else block:

```
error: missing condition for `if` statemementt push fork -f

  --> $DIR/issue-13483.rs:16:5
   |
13 |    } else if {
   |             ^ expected if condition here
```

instead of

```
error: expected `{`, found `else`
  --> ../../src/test/ui/issue-13483.rs:14:7
   |
14 |     } else {
   |       ^^^^
```

src/test/ui/issue-13483.rs

@@ -0,0 +1,22 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    if true {
+    } else if { //ERROR: MISSING CONDITIONAL
+    } else {
+    };
+}
+
+fn foo() {
+    if true {
+    } else if { //ERROR: MISSING CONDITIONAL
+    };
+}

src/test/ui/issue-13483.stderr

@@ -0,0 +1,14 @@
+error: missing condition for `if` statemement
+  --> $DIR/issue-13483.rs:13:14
+   |
+13 |     } else if { //ERROR: MISSING CONDITIONAL
+   |              ^ expected if condition here
+
+error: missing conditional
+  --> $DIR/issue-13483.rs:20:14
+   |
+20 |     } else if { //ERROR: MISSING CONDITIONAL
+   |              ^ expected if condition here
+
+error: aborting due to 2 previous errors
+