Poll before reading /proc/maps in process.libs() (#2516)

Try to avoid race condition of reading memory maps before libraries are loaded.

pwnlib/tubes/process.py

@@ -1323,7 +1323,7 @@ def libs(self):
         space.
         """
         from pwnlib.util.proc import memory_maps
-        maps_raw = memory_maps(self.pid)
+        maps_raw = self.poll() is not None and memory_maps(self.pid)
 
         if not maps_raw:
             import pwnlib.elf.elf