Plugin hi-jacking non-matching symbol text
**Description**
Currently experiencing some interesting behaviour using find and replace where non-matching items are being replaced with a series of numbers and dashes in the override sections of symbols, but only the ones without overriding text.

**Steps to produce:**
1. Have a symbol with overrides, some filled with overrides some with just the default text
2. Use this plugin to find and replace a term that does not exist in the symbol

Expected behaviour:
Matches are replaced (working).

**Actual behaviour:**
Matches are replaced but also specific non-matches are replaced each with unique series of numbers and dashes (described above).

**Notes:**
Have attached a screen shot of post find and replace. I have the breadcrumb selected which is where the issue is manifesting. Notice that the last two sections of the breadcrumb are filled with those series of numbers. Also can be seen in the left panel.

**Specs:**
Sketch Version: 52.2
OS: 10.4 

p.s. appreciate your work, great plugin. Will provide more details if I can and is useful.

<img width="1552" alt="findreplace" src="https://user-images.githubusercontent.com/44354398/47322052-5aba3980-d6a2-11e8-9b7d-78d0b3067503.png">
