rows: Throw exception instead of returning NaN.

We don't expect this to happen, and we don't want
to try to maintain the difficult task of gracefully
handling errors that we don't expect to happen
anyways. This will also make the conversion
to typescript easier.

web/src/rows.js

@@ -80,22 +80,14 @@ export function id($message_row) {
         return undefined;
     }
 
-    /*
-        For blueslip errors, don't return early, since
-        we may have some code now that actually relies
-        on the NaN behavior here.  We can try to clean
-        that up in the future, but we mainly just want
-        more data now.
-    */
-
     if ($message_row.length !== 1) {
-        blueslip.error("Caller should pass in a single row.");
+        throw new Error("Caller should pass in a single row.");
     }
 
     const zid = $message_row.attr("zid");
 
     if (zid === undefined) {
-        blueslip.error("Calling code passed rows.id a row with no zid attr.");
+        throw new Error("Calling code passed rows.id a row with no zid attr.");
     }
 
     return Number.parseFloat(zid);