fix: max-value overflow and explicit fast path for n_pts == 1

Author: mrtcnk

src/bulletproof_aggregated.c

@@ -1136,7 +1136,15 @@ static int calculate_commitment_term(
         pts[n_pts++] = &tH;
     }
 
-    return secp256k1_ec_pubkey_combine(ctx, out, pts, n_pts);
+    if (n_pts == 1) {
+        *out = *pts[0];
+        return 1;
+    }
+
+    if (!secp256k1_ec_pubkey_combine(ctx, out, pts, n_pts))
+        return 0;
+
+    return 1;
 }
 
 /**

tests/test_bulletproof_agg.c

@@ -129,7 +129,9 @@ void run_test_case(secp256k1_context* ctx, const char* name, uint64_t* values, s
     EXPECT(secp256k1_bulletproof_create_commitment(
             ctx,
             &bad_commitments[num_values - 1],
-            values[num_values - 1] + 1,
+            (values[num_values - 1] == UINT64_MAX)
+            ? values[num_values - 1] - 1
+            : values[num_values - 1] + 1,
             bad_blinding,
             &pk_base));