do not create extenstion symbol if extension does not exist

[flyerhzm]

for request like http://localhost/v1/test without .json at the end, it will create symbol :"/v1/test", which leads to memory leak

[jeltz]

To me the leak looks only like it is fixed for normal users. Malicious users should still be able to cause a memory leak by generating requests with random extensions.

[flyerhzm]

@jeltz you are right, the better way is not compare extension as symbol, use string instead.

I used grape to build an internal api service, so that's not a problem to me.

[dblock]

@jeltz - would you please be so kind to open an issue with maybe a repro for this? Thanks.

[dblock]

I opened #301.

[jeltz]

@dblock Thanks!

[dblock]

I found another instance where this is a problem, cookie processing.

Please double-check my fixes:

Cookie to_sym fix in df8665c
Formatter middleware to_sym fix in db7d190