Replace base64 decoding.

This code has caused a long history of problems. This change rewrites it
completely with something that is, hopefully, much simplier and robust
and adds more testing.

Change-Id: Ibeef51f9386afd95d5b73316e451eb3a2d7ec4e0
Reviewed-on: https://boringssl-review.googlesource.com/8033
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/fuzz/read_pem_corpus/4b32aa9edbd17b2d63390a41cc98739be7d45596 b/fuzz/read_pem_corpus/4b32aa9edbd17b2d63390a41cc98739be7d45596
new file mode 100644
index 0000000..0240c22
--- /dev/null
+++ b/fuzz/read_pem_corpus/4b32aa9edbd17b2d63390a41cc98739be7d45596
@@ -0,0 +1,7 @@
+-----BEGIN :°4'-----
+  f  uf  f -
+;3;w:,Ÿ=*'í3>;9:5ð;(°'çñØ*iØ)T'fµi'(;n*;;Ñ*?;¯Â-----
+-----END :°4'-----
+:$;(:!@;L)J‘))':ýZ:!ã:.6'y:*'*aíYXX;À‡:Ø()*!;Sß------BEGIN Û…:f(;w:;Å,Ÿ=*'í3>;9:°ç(ñð;µi'(;
+E=BEGI(N-----)GIԂ'Ð)*–::!!;!²>:r*>!oT#!>;):))†ä¸:pэ*òÄ;e÷' *(%ùy¬*'£;*'Ÿ(“d'!¥;Տï;æN 'µi'(;
+%i;;)''D;Û…:;;)j':'È;þ;ki!£ûš'!''D;Ûm!!Æ(£'4!$­!0*‘…
\ No newline at end of file