Easily fixed.
1. Shift the lever to the full forward position. The front derailleur will shift into the small chainring position.
2. Now disconnect the cable from the derailleur, pull it taut and reattach it.
3. The lever will now only move about 90 degrees because the high limit screw on the derailleur will stop it.
+1. With friction shifters (like your FD downtube shifter) you probably just have the cable too slack when the shift is let all the way out.
You can leave it like that so long as your shifter is still able to move enough to shift your FD to the high limit -- I don't know why your cable broke. That's a separate issue.