gh-37861: Fix segfault for Weil polynomials
    
Fix segfault for Weil polynomials

Eliminate a segfault that occurs when asking for Weil polynomials of
degree 0 and sign -1 (which do not exist, so the iterator should return
empty). This fixes #37860.
    
URL: #37861
Reported by: kedlaya
Reviewer(s): Travis Scrimshaw

Author: Release Manager

src/sage/rings/polynomial/weil/weil_polynomials.pyx

@@ -324,7 +324,7 @@ class WeilPolynomials_iter():
         if node_limit is None:
             node_limit = -1
         force_squarefree = Integer(squarefree)
-        self.process = dfs_manager(d2, q, coefflist, modlist, coeffsign,
+        self.process = None if d2<0 else dfs_manager(d2, q, coefflist, modlist, coeffsign,
                                    num_cofactor, node_limit, parallel,
                                    force_squarefree)
         self.q = q
@@ -537,7 +537,12 @@ class WeilPolynomials():
         sage: list(WeilPolynomials(10, 2, lead=(1,-3,5,-5,5,-5)))
         [x^10 - 3*x^9 + 5*x^8 - 5*x^7 + 5*x^6 - 5*x^5 + 10*x^4 - 20*x^3 + 40*x^2 - 48*x + 32]
 
+    Test that :issue:`37860` is resolved::
 
+        sage: list(WeilPolynomials(-1, 1))
+        []
+        sage: list(WeilPolynomials(0, 1, sign=-1))
+        []
     """
     def __init__(self, d, q, sign=1, lead=1, node_limit=None, parallel=False, squarefree=False, polring=None):
         r"""