Add two error codes to the Error module

One of the error codes was already reserved, this commit just makes it
explicit. The other one is a new error code for initializing return
values in the library: `MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED` should
not be returned by the library. If it is returned, then it is surely a
bug in the library or somebody is tampering with the device.
diff --git a/library/error.c b/library/error.c
index d8b5780..53b3a26 100644
--- a/library/error.c
+++ b/library/error.c
@@ -109,6 +109,10 @@
 #include "mbedtls/entropy.h"
 #endif
 
+#if defined(MBEDTLS_ERROR_C)
+#include "mbedtls/error.h"
+#endif
+
 #if defined(MBEDTLS_GCM_C)
 #include "mbedtls/gcm.h"
 #endif
@@ -754,6 +758,13 @@
         mbedtls_snprintf( buf, buflen, "ENTROPY - Read/write error in file" );
 #endif /* MBEDTLS_ENTROPY_C */
 
+#if defined(MBEDTLS_ERROR_C)
+    if( use_ret == -(MBEDTLS_ERR_ERROR_GENERIC_ERROR) )
+        mbedtls_snprintf( buf, buflen, "ERROR - Generic error" );
+    if( use_ret == -(MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED) )
+        mbedtls_snprintf( buf, buflen, "ERROR - This is a bug in the library" );
+#endif /* MBEDTLS_ERROR_C */
+
 #if defined(MBEDTLS_GCM_C)
     if( use_ret == -(MBEDTLS_ERR_GCM_AUTH_FAILED) )
         mbedtls_snprintf( buf, buflen, "GCM - Authenticated decryption failed" );