tfm fp_exptmod_nct: set result to zero when base is zero

Author: philljj

wolfcrypt/src/tfm.c

@@ -3171,8 +3171,10 @@ int fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
    int x = fp_count_bits (X);
 #endif
 
+   /* 0^X mod P = 0 mod P = 0.
+    * Set result to 0 and return early. */
    if (fp_iszero(G)) {
-      fp_set(G, 0);
+      fp_set(Y, 0);
       return FP_OKAY;
    }