Fix static build

MODULE_SUFFIX is undefined when building statically; don't used it.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
Patch status: sent upstream
(http://dovecot.org/pipermail/dovecot/2014-November/098694.html)

diff -Nuar dovecot-2.2.15-orig/src/lib/module-dir.c dovecot-2.2.15/src/lib/module-dir.c
--- dovecot-2.2.15-orig/src/lib/module-dir.c	2014-10-18 00:10:15.000000000 +0300
+++ dovecot-2.2.15/src/lib/module-dir.c	2014-11-13 19:27:29.417786313 +0200
@@ -621,7 +621,11 @@
 	if (*p == '_')
 		fname = p + 1;
 
+#ifdef MODULE_SUFFIX
 	p = strstr(fname, MODULE_SUFFIX);
+#else
+	p = NULL;
+#endif
 	if (p == NULL)
 		return fname;