Have secp256k1_ge_set_all_gej_var initialize all fields.

Previous behaviour would not initialize r->y values in the case where infinity is passed in.
Furthermore, the previous behaviour wouldn't initialize anything in the case where all inputs were infinity.

Author: roconnor-blockstream

src/group_impl.h

@@ -119,7 +119,9 @@ static void secp256k1_ge_set_all_gej_var(secp256k1_ge *r, const secp256k1_gej *a
     size_t last_i = SIZE_MAX;
 
     for (i = 0; i < len; i++) {
-        if (!a[i].infinity) {
+        if (a[i].infinity) {
+            secp256k1_ge_set_infinity(&r[i]);
+        } else {
             /* Use destination's x coordinates as scratch space */
             if (last_i == SIZE_MAX) {
                 r[i].x = a[i].z;
@@ -147,7 +149,6 @@ static void secp256k1_ge_set_all_gej_var(secp256k1_ge *r, const secp256k1_gej *a
     r[last_i].x = u;
 
     for (i = 0; i < len; i++) {
-        r[i].infinity = a[i].infinity;
         if (!a[i].infinity) {
             secp256k1_ge_set_gej_zinv(&r[i], &a[i], &r[i].x);
         }