Handle EINTR for io_uring

Fixes #26 specifically, we are still missing similar handling in other
places.

src/fellow_io_uring.c

@@ -541,6 +541,9 @@ fellow_io_wait_completions(fellow_ioctx_t *ctxp,
 		if (cb && advance)
 			cb(priv, results - advance, advance);
 
+		assert(ctx->outstanding >= advance);
+		ctx->outstanding -= advance;
+
 		/*
 		 * XXX if we are called from under a lock (for the multithreaded
 		 * case in fellow_cache.c) we should unlock while waiting,
@@ -560,12 +563,14 @@ fellow_io_wait_completions(fellow_ioctx_t *ctxp,
 		else
 			r = 0;
 
-		//lint -e{731} XXX
-		XXXAN(r >= 0);
+		if (r < 0) {
+			assert(errno == EINTR);
+			continue;
+		}
+
+		assert(r >= 0);
 		u = (typeof(u))r;
 
-		assert(ctx->outstanding >= advance);
-		ctx->outstanding -= advance;
 		assert(u <= ctx->unsubmitted);
 		ctx->outstanding += u;
 		ctx->unsubmitted -= u;