cljr-rename-symbol crashes for the first time on an unevaluated namespace (cljr-warn-on-eval 't)

Hi!

Cljr fails to rename symbol in code which is successfully compiled and run by`lein test`.

## Expected behavior

1. `cd /Users/YourName/Desktop`.
2. `git clone https://github.com/developer2019/example`
3. Open `/Users/YourName/Desktop/example/src/anagram.clj` in Emacs.
4. `M-x cider-mode`
5. ` `
6. Position cursor at `anagrams-for` (line 4, symbol 10) and press M-x `cljr-rename-symbol` RET.
It tells that project needs to be evaluated, type `y RET`.
7. Cljr should ask for a new symbol name and then rename this symbol in all project files.

## Actual behavior

1. `cd /Users/YourName/Desktop`.
2. `git clone https://github.com/developer2019/example`
3. Open `/Users/YourName/Desktop/example/src/anagram.clj in Emacs`.
4. `M-x cider-mode`
5. ` `
6. Position cursor at `anagrams-for` (line 4, symbol 10) and press M-x `cljr-rename-symbol` RET.
It tells that project needs to be evaluated, type `y RET`.
7. It fails with `Wrong type argument: char-or-string-p, nil`.

## Steps to reproduce the problem
1. `cd /Users/YourName/Desktop`.
2. `git clone https://github.com/developer2019/example`
3. Open `/Users/YourName/Desktop/example/src/anagram.clj in Emacs`.
4. `M-x cider-mode`
5. ` `
6. Position cursor at `anagrams-for` (line 4, symbol 10) and press M-x `cljr-rename-symbol` RET.
It tells that project needs to be evaluated, type `y RET`.
7. It fails with `Wrong type argument: char-or-string-p, nil`.

## Environment & Version information

`lein test` compiles this code and runs successfully.

### clj-refactor.el version information

clj-refactor 2.4.0-SNAPSHOT (package: 20171117.317), refactor-nrepl 2.4.0-SNAPSHOT from MELPA (i. e. latest clj-refactor).

### CIDER version information

```
;; CIDER 0.15.1 (London), nREPL 0.2.12
;; Clojure 1.8.0, Java 1.8.0_111
```

### Leiningen or Boot version
```
$ lein --version
Leiningen 2.8.1 on Java 1.8.0_111 Java HotSpot(TM) 64-Bit Server VM
```
`lein test` compiles this project and runs successfully.

### Emacs version

```
GNU Emacs 25.3.1
```

### Operating system
```
OS X 10.11 "El Capitan"
```