[libcalamares] Also report empty buffer as no-entropy

src/libcalamares/utils/Entropy.cpp

@@ -26,6 +26,11 @@ CalamaresUtils::EntropySource
 CalamaresUtils::getEntropy( int size, QByteArray& b )
 {
     b.clear();
+    if ( size < 1)
+    {
+        return EntropySource::None;
+    }
+
     b.resize( size );
     char* buffer = b.data();
     std::fill( buffer, buffer + size, 0xcb );

src/libcalamares/utils/Entropy.h

@@ -28,6 +28,7 @@ namespace CalamaresUtils
 /// @brief Which entropy source was actually used for the entropy.
 enum class EntropySource
 {
+    None,  ///< Buffer is empty, no random data
     URandom,  ///< Read from /dev/urandom
     Twister  ///< Generated by pseudo-random
 };