Bug report

the background box for a text object that is composed via latex with subscript can not be covered by the box if letting the padding of the box be equal to 0

ax.annotate(r'$A_{\tiny 1}$', xy=(0.5,0.5), bbox=dict(boxstyle='round,pad=0', fc='w', ec='none'))

Expected outcome : the text has a white background as small as possible and include all of the text

Actual outcome : the text always exceeds the bbox unless using a bigger padding that is ugly

Matplotlib version

• Operating system: windows 10 x64
• Matplotlib version: 3.0.2
• Matplotlib backend (print(matplotlib.get_backend())): tkagg
• Python version: 3.7.0
• Jupyter version (if applicable):
• Other libraries: