more defensive coding

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

ts/client/src/accounts/healthCache.ts

@@ -204,6 +204,15 @@ export class HealthCache {
       return ZERO_I80F48;
     }
 
+    if (
+      sourceBank.initLiabWeight
+        .sub(targetBank.initAssetWeight)
+        .abs()
+        .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).