[traceback] Fix "missing whitespace" bug

It turns out that we intentionally don't add such a whitespace at the beginning of the trace rendering, but we were actually doing so for the 2nd item of the stack rather than the 1st one

rich/traceback.py

@@ -584,7 +584,7 @@ def render_locals(frame: Frame) -> Iterable[ConsoleRenderable]:
                 )
                 excluded = False
 
-            first = frame_index == 1
+            first = frame_index == 0
             frame_filename = frame.filename
             suppressed = any(frame_filename.startswith(path) for path in self.suppress)
 

tests/test_traceback.py

@@ -1,4 +1,5 @@
 import io
+import re
 import sys
 
 import pytest
@@ -21,17 +22,48 @@
 def test_handler():
     console = Console(file=io.StringIO(), width=100, color_system=None)
     expected_old_handler = sys.excepthook
+
+    def level1():
+        level2()
+
+    def level2():
+        return 1 / 0
+
     try:
         old_handler = install(console=console)
         try:
-            1 / 0
+            level1()
         except Exception:
             exc_type, exc_value, traceback = sys.exc_info()
             sys.excepthook(exc_type, exc_value, traceback)
             rendered_exception = console.file.getvalue()
             print(repr(rendered_exception))
             assert "Traceback" in rendered_exception
             assert "ZeroDivisionError" in rendered_exception
+
+            frame_blank_line_possible_preambles = (
+                # Start of the stack rendering:
+                "╭─────────────────────────────── Traceback (most recent call last) ────────────────────────────────╮",
+                # Each subsequent frame (starting with the file name) should bthen e preceded with a blank line:
+                "│" + (" " * 98) + "│",
+            )
+            for frame_start in re.finditer(
+                "^│ .+rich/tests/test_traceback\.py:",
+                rendered_exception,
+                flags=re.MULTILINE,
+            ):
+                frame_start_index = frame_start.start()
+                for preamble in frame_blank_line_possible_preambles:
+                    preamble_start, preamble_end = (
+                        frame_start_index - len(preamble) - 1,
+                        frame_start_index - 1,
+                    )
+                    if rendered_exception[preamble_start:preamble_end] == preamble:
+                        break
+                else:
+                    pytest.fail(
+                        f"Frame {frame_start[0]} doesn't have the expected preamble"
+                    )
     finally:
         sys.excepthook = old_handler
         assert old_handler == expected_old_handler