BUG/MINOR: server: Don't call fopen() with server-state filepath set to NULL

When a local server-state file is loaded, if its name is too long, the error
is not properly handled, resulting to a call to fopen() with the "filepath"
variable set to NULL. To fix the bug, when this error occurs, we jump to the
next proxy, via a "continue" statement. And we take case to set "filepath"
variable after the error handling to be sure.

This patch should fix the issue #1111. It must be backported as far as 1.6.
diff --git a/src/server.c b/src/server.c
index e95580f..203e8ad 100644
--- a/src/server.c
+++ b/src/server.c
@@ -3372,10 +3372,10 @@
 					localfilepathlen += len;
 					localfilepath[localfilepathlen++] = 0;
 				}
-				filepath = localfilepath;
  localfileerror:
 				if (localfilepathlen == 0)
-					localfilepath[0] = '\0';
+					continue;
+				filepath = localfilepath;
 
 				break;
 			case PR_SRV_STATE_FILE_NONE: