wayland-server: Properly handle EAGAIN from wl_connection_read()

commit 3cddb3c692acd3536a7cc8542a29f0cc3c0ac3d6 casted len to an
unsigned value to compare to sizeof results.  However,
wl_connection_read() can fail, setting errno to EAGAIN and returning
a value of -1.

When cast to an unsigned type this leads to a loop condition of true
when it should be false.

Signed-off-by: Dipen Somani <dipen.somani@samsung.com>
Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>

src/wayland-server.c

diff --git a/src/wayland-server.c b/src/wayland-server.c
index eb1e500..eab2ee4 100644
--- a/src/wayland-server.c
+++ b/src/wayland-server.c
@@ -353,7 +353,7 @@
 		}
 	}
 
-	while ((size_t) len >= sizeof p) {
+	while (len >= 0 && (size_t) len >= sizeof p) {
 		wl_connection_copy(connection, p, sizeof p);
 		opcode = p[1] & 0xffff;
 		size = p[1] >> 16;