Skip call to memcpy if buffer length is zero

This allows the copy functions to work when passed a (NULL, 0) buffer.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index e03e2ae..43495e2 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -8462,7 +8462,9 @@
         return PSA_ERROR_CORRUPTION_DETECTED;
     }
 
-    memcpy(input_copy, input, input_len);
+    if (input_len > 0) {
+        memcpy(input_copy, input, input_len);
+    }
 
     return PSA_SUCCESS;
 }
@@ -8486,7 +8488,11 @@
     if (output_len < output_copy_len) {
         return PSA_ERROR_CORRUPTION_DETECTED;
     }
-    memcpy(output, output_copy, output_copy_len);
+
+    if (output_copy_len > 0) {
+        memcpy(output, output_copy, output_copy_len);
+    }
+
     return PSA_SUCCESS;
 }