simplify control flow in RestoreHelper methods

simplify control flow in RestoreHelper methods

Make the control flow more obvious. The code in question was
introduced with commit ea6d3c3e… but did not make sense back then
either because cur_index which is the constant $1$ was compared
to the literal constant $0$:

+        cur_index = 1
+        while cur_index < len(self._data):
+            data = self._data[cur_index]
…
+                if cur_index == 0:

This bogus test was since removed but the convoluted ``while``
loop survived. Instead, access index 1 only once using an integer
literal.