Catch a failed factorisation, using runtime error for now

The flint docs don't specify *when* this can fail so I'm not sure it fits with a DomainError or the like

Author: Jake-Moss

src/flint/types/fmpq_mpoly.pyx

@@ -924,7 +924,8 @@ cdef class fmpq_mpoly(flint_mpoly):
             fmpq_mpoly u
 
         fmpq_mpoly_factor_init(fac, self.ctx.val)
-        fmpq_mpoly_factor(fac, self.val, self.ctx.val)
+        if not fmpq_mpoly_factor(fac, self.val, self.ctx.val):
+            raise RuntimeError("factorisation failed")
         res = [0] * fac.num
 
         for i in range(fac.num):

src/flint/types/fmpz_mpoly.pyx

@@ -907,7 +907,8 @@ cdef class fmpz_mpoly(flint_mpoly):
             fmpz_mpoly u
 
         fmpz_mpoly_factor_init(fac, self.ctx.val)
-        fmpz_mpoly_factor(fac, self.val, self.ctx.val)
+        if not fmpz_mpoly_factor(fac, self.val, self.ctx.val):
+            raise RuntimeError("factorisation failed")
         res = [0] * fac.num
 
         for i in range(fac.num):