BUG/MINOR: config: .if/.elif should also accept negative integers

The doc about .if/.elif config block conditions says:

  a non-nul integer (e.g. '1'), always returns "true"

So we must accept negative integers as well. The test was made on
atoi() > 0.

No backport is needed, this is only 2.4.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index b6145fc..0048a12 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -1865,7 +1865,7 @@
 				} else if (!*args[1] || *args[1] == '0') {
 					/* empty = false */
 					nested_conds[nested_cond_lvl] = NESTED_COND_IF_DROP;
-				} else if (atoi(args[1]) > 0) {
+				} else if (atoi(args[1]) != 0) {
 					/* true */
 					nested_conds[nested_cond_lvl] = NESTED_COND_IF_TAKE;
 				} else {
@@ -1897,7 +1897,7 @@
 				} else if (!*args[1] || *args[1] == '0') {
 					/* empty = false */
 					nested_conds[nested_cond_lvl] = NESTED_COND_ELIF_DROP;
-				} else if (atoi(args[1]) > 0) {
+				} else if (atoi(args[1]) != 0) {
 					/* true */
 					nested_conds[nested_cond_lvl] = NESTED_COND_ELIF_TAKE;
 				} else {