Check each input for IsMine() in GetAddressGroupings

This commit fixes a crash from an out-of-range vector element access attempt
that stems from the same situation with Gridcoin as in the following Bitcoin
PR: bitcoin/bitcoin#1872.

Very strange our code did not already have this change.

src/wallet/wallet.cpp

@@ -2523,27 +2523,40 @@ set< set<CTxDestination> > CWallet::GetAddressGroupings()
 
         if (pcoin->vin.size() > 0 && (IsMine(pcoin->vin[0]) != ISMINE_NO))
         {
+            bool any_mine = false;
+
             // group all input addresses with each other
             for (auto const& txin : pcoin->vin)
             {
                 CTxDestination address;
-                if(!ExtractDestination(mapWallet[txin.prevout.hash].vout[txin.prevout.n].scriptPubKey, address))
-                    continue;
+
+                // If the input is not mine, ignore it.
+                if (IsMine(txin) == ISMINE_NO) continue;
+
+                CScript& scriptPubKey = mapWallet[txin.prevout.hash].vout[txin.prevout.n].scriptPubKey;
+
+                if (!ExtractDestination(scriptPubKey, address)) continue;
+
                 grouping.insert(address);
+                any_mine = true;
             }
 
             // group change with input addresses
-            for (auto const& txout : pcoin->vout)
-                if (IsChange(txout))
-                {
-                    CWalletTx tx = mapWallet[pcoin->vin[0].prevout.hash];
-                    CTxDestination txoutAddr;
-                    if(!ExtractDestination(txout.scriptPubKey, txoutAddr))
-                        continue;
-                    grouping.insert(txoutAddr);
-                }
-            groupings.insert(grouping);
-            grouping.clear();
+            if (any_mine) {
+                for (auto const& txout : pcoin->vout)
+                    if (IsChange(txout))
+                    {
+                        CTxDestination txoutAddr;
+                        if(!ExtractDestination(txout.scriptPubKey, txoutAddr))
+                            continue;
+                        grouping.insert(txoutAddr);
+                    }
+            }
+
+            if (grouping.size() > 0) {
+                groupings.insert(grouping);
+                grouping.clear();
+            }
         }
 
         // group lone addrs by themselves