Add test case for first intermediate max_pathlen=0

!!! This test case is currently failing !!!
(See fix in next-next commit.)

Test certificates generated with the following script:

programs/pkey/gen_key type=ec ec_curve=secp256r1 filename=cert81.key
programs/pkey/gen_key type=ec ec_curve=secp256r1 filename=cert82.key
programs/pkey/gen_key type=ec ec_curve=secp256r1 filename=cert83.key

programs/x509/cert_write serial=81 output_file=cert81.crt is_ca=1 \
    issuer_key=cert81.key issuer_name="CN=Root 8,O=mbed TLS,C=UK" \
    selfsign=1
programs/x509/cert_write serial=82 output_file=cert82.crt is_ca=1 \
    issuer_key=cert81.key issuer_name="CN=Root 8,O=mbed TLS,C=UK" \
    subject_key=cert82.key subject_name="CN=Int 82,O=mbed TLS,C=UK" \
    max_pathlen=0
programs/x509/cert_write serial=83 output_file=cert83.crt \
    issuer_key=cert82.key issuer_name="CN=Int 82,O=mbed TLS,C=UK" \
    subject_key=cert83.key subject_name="CN=EE 83,O=mbed TLS,C=UK"

mv cert8?.crt tests/data_files/dir4
rm cert8?.key

5 files changed, 41 insertions, 0 deletions

diff --git a/tests/data_files/dir4/Readme b/tests/data_files/dir4/Readme
index 5732a64..7217b75 100644
--- a/tests/data_files/dir4/Readme
+++ b/tests/data_files/dir4/Readme
@@ -36,3 +36,7 @@ cert61.crt (max_pathlen=1) -> cert62.crt -> cert63.crt
 cert71.crt (max_pathlen=1) -> cert72.crt -> cert73.crt (self signed) -> cert74.crt -> cert74.crt
 ```
 
+8. zero pathlen constraint on first intermediate CA (valid)
+```
+cert81.crt -> cert82.crt (max_pathlen=0) -> cert83.crt
+```
diff --git a/tests/data_files/dir4/cert81.crt b/tests/data_files/dir4/cert81.crt
new file mode 100644
index 0000000..26b2bd5
--- /dev/null
+++ b/tests/data_files/dir4/cert81.crt
@@ -0,0 +1,11 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
diff --git a/tests/data_files/dir4/cert82.crt b/tests/data_files/dir4/cert82.crt
new file mode 100644
index 0000000..d49ecc9
--- /dev/null
+++ b/tests/data_files/dir4/cert82.crt
@@ -0,0 +1,11 @@
+-----BEGIN CERTIFICATE-----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=
+-----END CERTIFICATE-----
diff --git a/tests/data_files/dir4/cert83.crt b/tests/data_files/dir4/cert83.crt
new file mode 100644
index 0000000..21a748e
--- /dev/null
+++ b/tests/data_files/dir4/cert83.crt
@@ -0,0 +1,11 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
diff --git a/tests/suites/test_suite_x509parse.data b/tests/suites/test_suite_x509parse.data
index a540db2..255c4e1 100644
--- a/tests/suites/test_suite_x509parse.data
+++ b/tests/suites/test_suite_x509parse.data
@@ -1156,6 +1156,10 @@ X509 CRT verify chain #8 (self signed maxpathlen root)
 depends_on:POLARSSL_SHA256_C:POLARSSL_RSA_C
 x509_crt_verify_chain:"data_files/dir4/cert61.crt data_files/dir4/cert63.crt data_files/dir4/cert62.crt":"data_files/dir4/cert61.crt":0
 
+X509 CRT verify chain #9 (self signed maxpathlen root)
+depends_on:POLARSSL_SHA256_C:POLARSSL_ECDSA_C:POLARSSL_ECP_DP_SECP256R1_ENABLED
+x509_crt_verify_chain:"data_files/dir4/cert83.crt data_files/dir4/cert82.crt":"data_files/dir4/cert81.crt":0
+
 X509 OID description #1
 x509_oid_desc:"2B06010505070301":"TLS Web Server Authentication"