only run sqlglot limit check when user sets a limit (#6530)

## 📝 Summary

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We would unecessarily run sqlglot parse even when a default limit is not
specified.
This improves perf, and is less annoying for fresh notebooks (do not
require multiple installation popups)

## 🔍 Description of Changes

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## 📋 Checklist

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guidelines](https://github.com/marimo-team/marimo/blob/main/CONTRIBUTING.md).
- [ ] For large changes, or changes that affect the public API: this
change was discussed or approved through an issue, on
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- [ ] I have added tests for the changes made.
- [x] I have run the code and verified that it works as expected.

Author: Light2Dark

marimo/_sql/sql.py

@@ -123,9 +123,11 @@ def sql(
     if df is None:
         return None
 
-    has_limit = _query_includes_limit(query)
+    has_limit = False
     try:
         default_result_limit = get_default_result_limit()
+        if default_result_limit is not None:
+            has_limit = _query_includes_limit(query)
     except OSError:
         default_result_limit = None