[OPTIM] config: only allocate check buffer when checks are enabled

To save a little memory, the check_data buffer is only allocated
for the servers that are checked.

[WT: this patch saves 80 MB of RAM on the test config with 5000 servers]
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 680b546..0e414d0 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -3116,12 +3116,6 @@
 			newsrv->curfd = -1;		/* no health-check in progress */
 			newsrv->health = newsrv->rise;	/* up, but will fall down at first failure */
 
-			/* Allocate buffer for partial check results... */
-			if ((newsrv->check_data = calloc(BUFSIZE, sizeof(char))) == NULL) {
-				Alert("parsing [%s:%d] : out of memory while allocating check buffer.\n", file, linenum);
-				err_code |= ERR_ALERT | ERR_ABORT;
-				goto out;
-			}
 			cur_arg = 3;
 		} else {
 			newsrv = &curproxy->defsrv;
@@ -3563,6 +3557,13 @@
 				goto out;
 			}
 
+			/* Allocate buffer for partial check results... */
+			if ((newsrv->check_data = calloc(BUFSIZE, sizeof(char))) == NULL) {
+				Alert("parsing [%s:%d] : out of memory while allocating check buffer.\n", file, linenum);
+				err_code |= ERR_ALERT | ERR_ABORT;
+				goto out;
+			}
+
 			newsrv->check_status = HCHK_STATUS_INI;
 			newsrv->state |= SRV_CHECKED;
 		}