Check return value of write function

This patch closes the file descriptor and returns with a failure,
when there is a failure.

lib/shmem.cpp

@@ -339,7 +339,10 @@ int create_shmem_mmap(const char *path, size_t size, void** pp) {
         // area to all zeros because they write beyond the old EOF. 
         // See the lseek man page for details.
         lseek(fd, size-1, SEEK_SET);
-        write(fd, "\0", 1);
+        if (1 != write(fd, "\0", 1)) {
+	    close(fd);
+	    return ERR_SHMGET;
+	}
     }
 
     *pp = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, 0);