Trac #33640: sage fails to factor some easy expressions

As reported on [https://groups.google.com/g/sage-
devel/c/Ca661TP_3Ug/m/f2lZtUXLAwAJ sage-devel], sage fails to factor
expressions that expand to something very easy, such as `x^2` or `0`.
Instead, it returns the original expression.
{{{
sage: ((x + 1)^2 - 2*x - 1).factor()  # bad (should be x^2)
(x + 1)^2 - 2*x - 1
sage: ((x + 1)^2 - x^2 - 2*x - 1).factor()  # bad (should be 0)
(x + 1)^2 - x^2 - 2*x - 1
sage: ((x + 2)^2 - 2*x - 3).factor()  # good
(x + 1)^2
}}}

URL: https://trac.sagemath.org/33640
Reported by: gh-DaveWitteMorris
Ticket author(s): Frédéric Chapoton
Reviewer(s): David Lowry-Duda

src/sage/symbolic/expression.pyx

@@ -11898,6 +11898,11 @@ cdef class Expression(Expression_abc):
             x + sqrt(x)
             sage: factor((x + sqrt(x))/(x - sqrt(x)))
             (x + sqrt(x))/(x - sqrt(x))
+
+        Check that :trac:`33640` is fixed::
+
+            sage: ((x + 1)^2 - 2*x - 1).factor() 
+            x^2
         """
         from sage.calculus.calculus import symbolic_expression_from_maxima_string
         cdef GEx x

src/sage/symbolic/ginac/normal.cpp

@@ -1221,8 +1221,6 @@ bool factor(const ex& the_ex, ex& res_ex)
         den = normalized.op(1);
         ex res_den;
         bool dres = factorpoly(den, res_den);
-        if (not nres and not dres)
-                return false;
         if (not nres)
                 res_ex = num;
         if (not dres)