Store zmq_timers_timeout() result in long, not int (#681)

[why]
When compiling with -Wconversion, gcc 13.3 issues a warning:

zmq.hpp: In member function ‘zmq::timers::timeout_result_t zmq::timers::timeout() const’:
zmq.hpp:2857:41: warning: conversion from ‘long int’ to ‘int’ may change value [-Wconversion]
 2857 |         int timeout = zmq_timers_timeout(_timers);
      |                       ~~~~~~~~~~~~~~~~~~^~~~~~~~~

zmq_timers_timeout() returns long, but its return value is stored in an
int variable, which may or may not be a mismatch depending on compiler
and architecture.

[how]
Simply adjust the type of the variable from int to long. We could also
change the literal in the following comparison from -1 to -1L, but that
seems pedantic and does not match the style of the surrounding code.

Signed-off-by: Lars Froehlich <[email protected]>

Author: alt-graph

zmq.hpp

@@ -2928,7 +2928,7 @@ class timers
 
     timeout_result_t timeout() const
     {
-        int timeout = zmq_timers_timeout(_timers);
+        long timeout = zmq_timers_timeout(_timers);
         if (timeout == -1)
             return timeout_result_t{};
         return std::chrono::milliseconds{timeout};