Add handlers for parameter validation in the sample programs

The sample programs require an additional handler function of
mbedtls_param_failed() to handle any failed parameter validation checks enabled
by the MBEDTLS_CHECK_PARAMS config.h option.
diff --git a/programs/aes/aescrypt2.c b/programs/aes/aescrypt2.c
index 5725eb0..522bfda 100644
--- a/programs/aes/aescrypt2.c
+++ b/programs/aes/aescrypt2.c
@@ -78,6 +78,16 @@
     return( 0 );
 }
 #else
+
+#if defined( MBEDTLS_CHECK_PARAMS ) && defined(MBEDTLS_PLATFORM_C)
+void mbedtls_param_failed( char* failure_condition, char* file, int line )
+{
+    mbedtls_printf("%s:%i: Input param failed - %s\n", file, line,
+                   failure_condition );
+    mbedtls_exit( MBEDTLS_EXIT_FAILURE );
+}
+#endif
+
 int main( int argc, char *argv[] )
 {
     int ret = 0;
@@ -109,6 +119,7 @@
       off_t filesize, offset;
 #endif
 
+    mbedtls_aes_init( NULL );
     mbedtls_aes_init( &aes_ctx );
     mbedtls_md_init( &sha_ctx );