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/78e4c8a5d73cf074f243ef12a3669fef1e848121 b/fuzz/read_pem_corpus/78e4c8a5d73cf074f243ef12a3669fef1e848121
new file mode 100644
index 0000000..890697e
--- /dev/null
+++ b/fuzz/read_pem_corpus/78e4c8a5d73cf074f243ef12a3669fef1e848121
@@ -0,0 +1,10 @@
+-----BEGIN O-----
+----(END /!-----BEGI 7í‘;!(;)š-----END ç/O!:š-----BEGIN O-----
+----(END /!---'U('ß(:(ç/!;!;‘6í();':(´'H('G)M˜G¿ëÑ'yO-
+	)o(*(Ç*Ä;ò¹:)·¬Ù*ª:!:Œ:(';±×'Ú(;—é)Ð(!:™)¢í:”"P•Z ˆg;:; :':Â:7!)÷ö)vôǾ:--BEGIN 6í‘;!(;)š--
+----END ç/!-----
+-
+kqU;O!:š'U|:؎8*:;sá(f!‘;;)--*----
+----BEGIN ‘O-----
+----(END /!-----BEGIN 6í-
+j*:‘;!(;)š-----END 6çí(
\ No newline at end of file