No check if DataFrame is empty
```
Traceback (most recent call last):
  File "terminal.py", line 223, in <module>
    main()
  File "terminal.py", line 123, in main
    s_ticker, (datetime.now() - timedelta(days=180)).strftime("%Y-%m-%d")
  File "C:\\Users\\L\\Documents\\GamestonkTerminal\\gamestonk_terminal\\main_helper.py", line 231, in candle
    df_stock = trend.load_ticker(s_ticker, s_start)
  File "C:\\Users\\L\\Documents\\GamestonkTerminal\\gamestonk_terminal\\fundamental_analysis\\trendline_api.py", line 26, in load_ticker
    df_data = yf.download(ticker, start=start_date, progress=False)
  File "C:\\Users\\L\\AppData\\Roaming\\Python\\Python37\\site-packages\\yfinance\\multi.py", line 127, in download
    keys=shared._DFS.keys())
  File "C:\\Users\\L\\AppData\\Local\\Programs\\Python\\Python37\\lib\\site-packages\\pandas\\core\\reshape\\concat.py", line 284, in concat
    sort=sort,
  File "C:\\Users\\L\\AppData\\Local\\Programs\\Python\\Python37\\lib\\site-packages\\pandas\\core\\reshape\\concat.py", line 331, in __init__
    raise ValueError("No objects to concatenate")
ValueError: No objects to concatenate
```

I ran  `candle abna` which I think might be a wrong stock symbol.
diff --git a/terminal.py b/terminal.py
index e30805c294..0d114f028f 100644
--- a/terminal.py
+++ b/terminal.py
@@ -119,12 +119,29 @@ def main():
             main_cmd = True
 
         elif ns_known_args.opt == "candle":
-            candle(
-                s_ticker, (datetime.now() - timedelta(days=180)).strftime("%Y-%m-%d")
-            )
+
+            if s_ticker:
+                candle(
+                    s_ticker,
+                    (datetime.now() - timedelta(days=180)).strftime("%Y-%m-%d"),
+                )
+
+            else:
+                print(
+                    "No ticker selected. Use 'load ticker' to load the ticker you want to look at."
+                )
+
+            main_cmd = True
 
         elif ns_known_args.opt == "view":
-            view(l_args, s_ticker, s_start, s_interval, df_stock)
+
+            if s_ticker:
+                view(l_args, s_ticker, s_start, s_interval, df_stock)
+
+            else:
+                print(
+                    "No ticker selected. Use 'load ticker' to load the ticker you want to look at."
+                )
             main_cmd = True
 
         elif ns_known_args.opt == "export":
['terminal.py']