renderPM can't set font

Since the `gsfonts` dependency was removed in bug #1862641, some reportlab functionalities are failing.

It can be reproduced with a simple example. First, ensure that `gsfonts` package is not installed.

In python3:

```
from reportlab.graphics.barcode import createBarcodeDrawing
barcode = createBarcodeDrawing('EAN13', value='1234')
barcode.asString('png')
```

This leads to the following traceback:
```
Warn: Can't find .pfb for face 'Times-Roman'
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 242, in _setFont
    gs.setFont(fontName,fontSize)
ValueError: _renderPM.gstate_setFont: Can't find font!

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 248, in _setFont
    _renderPM.makeT1Font(fontName,f.face.findT1File(),f.encoding.vector,open_and_read)
TypeError: makeT1Font() argument 2 must be str, not None

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/reportlab/graphics/shapes.py", line 854, in asString
    return renderPM.drawToString(self, fmt=format,showBoundary=getattr(self,'showBorder',
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 685, in drawToString
    drawToFile(d,s,fmt=fmt, dpi=dpi, bg=bg, configPIL=configPIL)
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 680, in drawToFile
    c = drawToPMCanvas(d, dpi=dpi, bg=bg, configPIL=configPIL, showBoundary=showBoundary)
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 666, in drawToPMCanvas
    draw(d, c, 0, 0, showBoundary=showBoundary)
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 51, in draw
    R.draw(renderScaledDrawing(drawing), canvas, x, y, showBoundary=showBoundary)
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderbase.py", line 204, in draw
    self.initState(x,y) #this is the push()
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 98, in initState
    self.applyState()
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 92, in applyState
    self._canvas.setFont(s['fontName'], s['fontSize'])
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 399, in setFont
    _setFont(self._gs,fontName,fontSize)
  File "/usr/lib/python3/dist-packages/reportlab/graphics/renderPM.py", line 251, in _setFont
    raise RenderPMError("Can't setFont(%s) missing the T1 files?\nOriginally %s: %s" % (fontName,s1,s2))
reportlab.graphics.renderPM.RenderPMError: Can't setFont(Times-Roman) missing the T1 files?
Originally <class 'TypeError'>: makeT1Font() argument 2 must be str, not None
```

After installing the `gsfonts` package, the traceback does not occurs and the code works as expected.

lsb release: Ubuntu 20.04.1 LTS
python3-renderpm:amd64 3.5.34-1ubuntu1