syntax: Fix pythonRawBytes prefix

Author: nfnty

syntax/python.vim

@@ -222,10 +222,10 @@ else
   syn region pythonRawString  start=+[rR]'''+ skip=+\\'+ end=+'''+ keepend contains=pythonDocTest,pythonSpaceError,@Spell
   syn region pythonRawString  start=+[rR]"""+ skip=+\\"+ end=+"""+ keepend contains=pythonDocTest2,pythonSpaceError,@Spell
 
-  syn region pythonRawBytes  start=+[bB][rR]'+ skip=+\\\\\|\\'\|\\$+ excludenl end=+'+ end=+$+ keepend contains=pythonRawEscape,@Spell
-  syn region pythonRawBytes  start=+[bB][rR]"+ skip=+\\\\\|\\"\|\\$+ excludenl end=+"+ end=+$+ keepend contains=pythonRawEscape,@Spell
-  syn region pythonRawBytes  start=+[bB][rR]'''+ skip=+\\'+ end=+'''+ keepend contains=pythonDocTest,pythonSpaceError,@Spell
-  syn region pythonRawBytes  start=+[bB][rR]"""+ skip=+\\"+ end=+"""+ keepend contains=pythonDocTest2,pythonSpaceError,@Spell
+  syn region pythonRawBytes  start=+\%([bB][rR]\|[rR][bB]\)'+ skip=+\\\\\|\\'\|\\$+ excludenl end=+'+ end=+$+ keepend contains=pythonRawEscape,@Spell
+  syn region pythonRawBytes  start=+\%([bB][rR]\|[rR][bB]\)"+ skip=+\\\\\|\\"\|\\$+ excludenl end=+"+ end=+$+ keepend contains=pythonRawEscape,@Spell
+  syn region pythonRawBytes  start=+\%([bB][rR]\|[rR][bB]\)'''+ skip=+\\'+ end=+'''+ keepend contains=pythonDocTest,pythonSpaceError,@Spell
+  syn region pythonRawBytes  start=+\%([bB][rR]\|[rR][bB]\)"""+ skip=+\\"+ end=+"""+ keepend contains=pythonDocTest2,pythonSpaceError,@Spell
 endif
 
 syn match pythonRawEscape +\\['"]+ display transparent contained