return 0 for swap from same source to same target

Signed-off-by: microwavedcola1 <microwavedcola@gmail.com>

ts/client/src/accounts/mangoAccount.ts

@@ -234,6 +234,10 @@ export class MangoAccount {
     targetTokenName: string,
     slippageAndFeesFactor: number,
   ): I80F48 {
+    if (sourceTokenName === targetTokenName) {
+      return ZERO_I80F48;
+    }
+
     return this.accountData.healthCache
       .getMaxSourceForTokenSwap(
         group,

ts/client/src/debug-scripts/mb-debug-user.ts

@@ -91,6 +91,7 @@ async function debugUser(client, group, mangoAccount) {
     );
   }
   getMaxSourceForTokenSwapWrapper('SOL', 'BTC');
+  getMaxSourceForTokenSwapWrapper('USDC', 'USDC');
 }
 
 async function main() {