Issue #21090: io.FileIO.readall() does not ignore I/O errors anymore. Before,
it ignored I/O errors if at least the first C call read() succeed.
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 58b68b6..6890ec3 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -577,9 +577,9 @@
                 }
                 continue;
             }
-            if (total > 0)
-                break;
             if (errno == EAGAIN) {
+                if (total > 0)
+                    break;
                 Py_DECREF(result);
                 Py_RETURN_NONE;
             }