defensive code

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

ts/client/src/accounts/healthCache.ts

@@ -196,6 +196,14 @@ export class HealthCache {
     const sourceBank = group.banksMap.get(sourceTokenName);
     const targetBank = group.banksMap.get(targetTokenName);
 
+    if (sourceTokenName === targetTokenName) {
+      return ZERO_I80F48;
+    }
+
+    if (!sourceBank.price || sourceBank.price.lte(ZERO_I80F48)) {
+      return ZERO_I80F48;
+    }
+
     // The health_ratio is a nonlinear based on swap amount.
     // For large swap amounts the slope is guaranteed to be negative, but small amounts
     // can have positive slope (e.g. using source deposits to pay back target borrows).

ts/client/src/accounts/mangoAccount.ts

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