Match to USA if no exchange suffix is present (#1939)

The logic on line 213 defaults to USA if there is no exchange symbol present, so the market coverage suffix should use the same logic. This enables filtering by exchange to work correctly.

Co-authored-by: didierlopes.eth <dro.lopes@campus.fct.unl.pt>

openbb_terminal/stocks/stocks_helper.py

@@ -43,7 +43,7 @@
 SOURCES = ["yf", "av", "iex"]
 
 market_coverage_suffix = {
-    "USA": ["CBT", "CME", "NYB", "CMX", "NYM"],
+    "USA": ["CBT", "CME", "NYB", "CMX", "NYM", ""],
     "Argentina": ["BA"],
     "Austria": ["VI"],
     "Australia": ["AX"],