Use the first valid line when parsing pdftex.map.

This can be tested by placing two lines with the same `tfmname`, but
different `psname` in a `pdftex.map`:

```
cmr12 CMR10 <cmr12.pfb
cmr12 CMR12 <cmr12.pfb
```

and then running `TEXFONTMAPS=/path/to/pdftex.map pdflatex` on a file
using Computer Modern. It will warn about the second line, and embed
`CMR10` as the name in the resulting PDF.

Author: QuLogic

lib/matplotlib/dviread.py

@@ -828,14 +828,19 @@ def __new__(cls, filename):
         # store the unparsed lines (keyed by the first word, which is the
         # texname) and parse them on-demand.
         with open(filename, 'rb') as file:
-            self._unparsed = {line.split(b' ', 1)[0]: line for line in file}
+            self._unparsed = {}
+            for line in file:
+                tfmname = line.split(b' ', 1)[0]
+                self._unparsed.setdefault(tfmname, []).append(line)
         self._parsed = {}
         return self
 
     def __getitem__(self, texname):
         assert isinstance(texname, bytes)
         if texname in self._unparsed:
-            self._parse_and_cache_line(self._unparsed.pop(texname))
+            for line in self._unparsed.pop(texname):
+                if self._parse_and_cache_line(line):
+                    break
         try:
             return self._parsed[texname]
         except KeyError:
@@ -920,6 +925,7 @@ def _parse_and_cache_line(self, line):
         self._parsed[tfmname] = PsFont(
             texname=tfmname, psname=basename, effects=effects,
             encoding=encodingfile, filename=fontfile)
+        return True
 
 
 # Note: this function should ultimately replace the Encoding class, which

lib/matplotlib/tests/baseline_images/dviread/test.map

@@ -8,3 +8,6 @@ TeXfont6 PSfont6
 TeXfont7 PSfont7 < font7.enc
 TeXfont8 PSfont8 <<font8.pfb
 TeXfont9 </absolute/font9.pfb
+% Only the first of a duplicate key is used.
+TeXfontA PSfontA1
+TeXfontA PSfontA2

lib/matplotlib/tests/test_dviread.py

@@ -44,6 +44,9 @@ def test_PsfontsMap(monkeypatch):
     entry = fontmap[b'TeXfont9']
     assert entry.psname == b'TeXfont9'
     assert entry.filename == b'/absolute/font9.pfb'
+    # First of duplicates only.
+    entry = fontmap[b'TeXfontA']
+    assert entry.psname == b'PSfontA1'
     # Missing font
     with pytest.raises(KeyError, match='no-such-font'):
         fontmap[b'no-such-font']