Fix bsv 20 lock neg supply.

src/contracts/bsv20Mint.ts

@@ -55,18 +55,21 @@ export class BSV20Mint extends BSV20V2 {
         // Check mint amount doesn't exceed maximum.
         assert(amount <= this.maxMintAmount, 'mint amount exceeds maximum')
 
-        // Update supply.
-        this.supply -= amount
-
-        // If there are still tokens left, then
-        // build state output inscribed with leftover tokens.
         let outputs = toByteString('')
+        let transferAmt = amount
+
         if (this.supply > 0n) {
+            // If there are still tokens left, then update supply and
+            // build state output inscribed with leftover tokens.
+            this.supply -= transferAmt
             outputs += this.buildStateOutputFT(this.supply)
+        } else {
+            // If not, then transfer all the remaining supply.
+            transferAmt = this.supply
         }
 
         // Build FT P2PKH output to dest paying specified amount of tokens.
-        outputs += BSV20V2.buildTransferOutput(dest, this.id, amount)
+        outputs += BSV20V2.buildTransferOutput(dest, this.id, transferAmt)
 
         // Build change output.
         outputs += this.buildChangeOutput()