Problem: valgrind shows unitialised errors in backtrace print

Solution: fix them

src/err.cpp

@@ -415,6 +415,10 @@ void zmq::print_backtrace (void)
         if (unw_get_proc_info (&cursor, &p_info))
             break;
 
+        rc = unw_get_proc_name (&cursor, func_name, 256, &offset);
+        if (rc == -UNW_ENOINFO)
+            strcpy(func_name, "?");
+
         addr = (void *)(p_info.start_ip + offset);
 
         if (dladdr (addr, &dl_info) && dl_info.dli_fname)
@@ -422,10 +426,6 @@ void zmq::print_backtrace (void)
         else
             file_name = "?";
 
-        rc = unw_get_proc_name (&cursor, func_name, 256, &offset);
-        if (rc == -UNW_ENOINFO)
-            strcpy(func_name, "?");
-
         demangled_name = abi::__cxa_demangle (func_name, NULL, NULL, &rc);
 
         printf ("#%u  %p in %s (%s+0x%lx)\n", frame_n++, addr, file_name,