util: fix virBitmap allocation in virProcessInfoGetAffinity

Found by coverity:
Error: REVERSE_INULL (CWE-476):
    libvirt-0.10.2/src/util/processinfo.c:141: deref_ptr: Directly
    dereferencing pointer "map".
    libvirt-0.10.2/src/util/processinfo.c:142: check_after_deref:
    Null-checking "map" suggests that it may be null, but it has already
    been dereferenced on all paths leading to the check.

src/util/processinfo.c

@@ -140,7 +140,7 @@ realloc:
     }
 
     *map = virBitmapNew(maxcpu);
-    if (!map) {
+    if (!*map) {
         virReportOOMError();
         return -1;
     }