wispr: Use g_strdup() instead of strdup()

wispr: Use g_strdup() instead of strdup()

Valgrind reports following error if strdup() is used here:

==12572== Invalid read of size 4
==12572==    at 0x429113B: ??? (in /lib/libc-2.11.90.so)
==12572==    by 0x80A8154: wispr_route_request (wispr.c:471)
==12572==    by 0x805CA4F: resolv_result (gweb.c:449)
==12572==    by 0x805DD4B: sort_and_return_results (gresolv.c:494)
==12572==    by 0x805E285: received_udp_data (gresolv.c:705)
==12572==    by 0x40AD8E6: ??? (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x4078AFA: g_main_context_dispatch (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x407911E: ??? (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x40796BC: g_main_loop_run (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x807400F: main (main.c:508)
==12572==  Address 0x55f406c is 20 bytes inside a block of size 22 alloc'd
==12572==    at 0x4029AE9: malloc (vg_replace_malloc.c:236)
==12572==    by 0x40B1D6C: g_malloc (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x40B4C25: g_strdup (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x805CA23: resolv_result (gweb.c:1222)
==12572==    by 0x805DD4B: sort_and_return_results (gresolv.c:494)
==12572==    by 0x805E285: received_udp_data (gresolv.c:705)
==12572==    by 0x40AD8E6: ??? (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x4078AFA: g_main_context_dispatch (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x407911E: ??? (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x40796BC: g_main_loop_run (in /lib/libglib-2.0.so.0.2800.6)
==12572==    by 0x807400F: main (main.c:508)
==12572==

If g_strdup() is used then no error is printed.
This error does not make much sense but anyway use g_strdup()
like in other parts of this file.