Initialise return values to an error

Initialising the return values to and error is best practice and makes
the library more robust.
diff --git a/library/platform.c b/library/platform.c
index 5756159..420d09e 100644
--- a/library/platform.c
+++ b/library/platform.c
@@ -29,6 +29,7 @@
 
 #include "mbedtls/platform.h"
 #include "mbedtls/platform_util.h"
+#include "mbedtls/error.h"
 
 /* The compile time configuration of memory allocation via the macros
  * MBEDTLS_PLATFORM_{FREE/CALLOC}_MACRO takes precedence over the runtime
@@ -86,7 +87,7 @@
 #include <stdarg.h>
 int mbedtls_platform_win32_snprintf( char *s, size_t n, const char *fmt, ... )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     va_list argp;
 
     va_start( argp, fmt );
@@ -131,7 +132,7 @@
 #include <stdarg.h>
 int mbedtls_platform_win32_vsnprintf( char *s, size_t n, const char *fmt, va_list arg )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
     /* Avoid calling the invalid parameter handler by checking ourselves */
     if( s == NULL || n == 0 || fmt == NULL )