relic_pc: gt_exp fails for zero exponent

[1gn1t10n]

Context

RELIC version: 1d08528
Configure parameters: -DDEBUG=on -DBENCH=10 -DTESTS=10 -DARITH=gmp -DALLOC=DYNAMIC -DBN_PRECI=8192 -DFP_PRIME=256

Reproduction

diff --git a/test/test_pc.c b/test/test_pc.c
index 041d1b2..7a19b11 100755
--- a/test/test_pc.c
+++ b/test/test_pc.c
@@ -1241,6 +1247,14 @@ int exponentiation(void) {
                        TEST_ASSERT(gt_is_unity(c), end);
                }
                TEST_END;
+
+         TEST_BEGIN("EXTRA gt_exp(a, 0)") {
+                 gt_rand(a);
+                 bn_set_dig(n, 0);
+                 gt_exp(c, a, n);
+                 TEST_ASSERT(gt_is_unity(c), end);
+         }
+         TEST_END;
        }
        CATCH_ANY {
                util_print("FATAL ERROR!\n");

Result: Segmentation fault
Expected result: a^0 == identity element in G_T

[dfaranha]

This specific issue should have been fixed by now!