Try known extensions in file with dots in the name (fixes #355)

This changes the behaviour when searching graphics files and both
'file.exta' and 'file.exta.extb' exist, and 'exta' is not a known
graphics extension.  In that case, the list of known extensions is
searched, and if 'extb' is valid, that file is tried instead.

Author: PhelypeOleinik

required/graphics/graphics.dtx

@@ -25,7 +25,7 @@
 %<driver> \ProvidesFile{graphics.drv}
 % \fi
 %         \ProvidesFile{graphics.dtx}
-          [2020/08/09 v1.4b  Standard LaTeX Graphics (DPC,SPQR)]
+          [2020/08/30 v1.4c  Standard LaTeX Graphics (DPC,SPQR)]
 %
 % \iffalse
 %<*driver>
@@ -1134,30 +1134,40 @@
   \else
     \Gin@getbase{\Gin@sepdefault\filename@ext}%
 %    \end{macrocode}
-% At this point try adding an extension, even if the filename has one so
-% that \verb|a.b| may find \verb|a.b.png| if no file is found then revert
-% to the extension as given to get better error reporting.
+% At this point try adding an extension, either if the given file name
+% has none, or if the extension matches no existing graphics inclusion
+% rule, so that \verb|a.b| may find \verb|a.b.png|, if only the latter
+% or if both files exist. If no file is found then revert to the
+% extension as given to get better error reporting.
 %
 % \changes{v1.3d}{2019/11/01}
-%     {Try adding an extension even if the filenam had a dot.}
-%    \begin{macrocode}
-\ifx\Gin@ext\relax
-\let\Gin@savedbase\filename@base
-\let\Gin@savedext\filename@ext
-  \edef\filename@base{\filename@base\Gin@sepdefault\filename@ext}%
-  \let\filename@ext\relax
-   \@for\Gin@temp:=\Gin@extensions\do{%
-      \ifx\Gin@ext\relax
-        \Gin@getbase\Gin@temp
-      \fi}%
-%    \end{macrocode}
-% Restore if no file found using theknown extensions.
+%     {Try adding an extension even if the filename had a dot.}
+% \changes{v1.4c}{2020/08/30}
+%     {Try adding an extension even if the filename had a dot AND
+%      if the filename without the extension exists (but doesn't have
+%      a known extension).}
+%    \begin{macrocode}
+    \ifnum0%
+        \ifx\Gin@ext\relax 1%
+        \else \@ifundefined{Gin@rule@\Gin@ext}{1}{0}%
+        \fi >0
+      \let\Gin@ext\relax
+      \let\Gin@savedbase\filename@base
+      \let\Gin@savedext\filename@ext
+      \edef\filename@base{\filename@base\Gin@sepdefault\filename@ext}%
+      \let\filename@ext\relax
+      \@for\Gin@temp:=\Gin@extensions\do{%
+          \ifx\Gin@ext\relax
+            \Gin@getbase\Gin@temp
+          \fi}%
+%    \end{macrocode}
+% Restore if no file found using the known extensions.
 %    \begin{macrocode}
-  \ifx\Gin@ext\relax
-    \let\filename@base\Gin@savedbase
-    \let\filename@ext\Gin@savedext
-  \fi
-\fi
+      \ifx\Gin@ext\relax
+        \let\filename@base\Gin@savedbase
+        \let\filename@ext\Gin@savedext
+      \fi
+    \fi
 %    \end{macrocode}
 %
 %    \begin{macrocode}