Fix undefined method error

[FixRM rapid7#8323]

Author: wchen-r7

modules/auxiliary/scanner/oracle/xdb_sid_brute.rb

@@ -242,7 +242,7 @@ def run_host(ip)
 				}
 			}, -1)
 
-			if (res.code == 200)
+			if res and res.code == 200
 				if (not res.body.length > 0)
 				# sometimes weird bug where body doesn't have value yet
 					res.body = res.bufq
@@ -294,7 +294,7 @@ def run_host(ip)
 				}
 			}, -1)
 
-			if (res.code == 200)
+			if res and res.code == 200
 				if (not res.body.length > 0)
 				# sometimes weird bug where body doesn't have value yet
 					res.body = res.bufq