Update thread_queue.h to remove conflict with windows headers

[mcgi5sr2]

Add parenthesis around MAX_CAPACITY evaluation to ensure it is not misinterpreted as a macro when using windows headers

First came across this when trying to compile with libcurl headers (curl/curl.h).

[fpagliughi]

What is this colliding with? A max macro?

[mcgi5sr2]

yes exactly that

[mcgi5sr2]

Apologies I have been hard at another project. The issue is given by VS studio as a warning:
Warning C4003 not enough arguments for function-like macro invocation 'max' mqtt_no_http ****\include\mqtt\thread_queue.h 96

followed by errors '(': illegal token on right side of'::' a couple of syntax errors about brackets and then:

missing type specifier - int assumed. Note: C++ does not support default-int

To reproduce I think it should be enough to include curl/curl.h in your simple subscriber example.

I get the PR isn't a tidy resolution but it seemed to be the simplest.

[fpagliughi]

No worries; I'm busy on something else as well, but I will look into it as soon as I can.