Fix a compiler warning

Signed-off-by: falkTX <falktx@falktx.com>

distrho/extra/String.hpp

@@ -695,7 +695,7 @@ public:
             "abcdefghijklmnopqrstuvwxyz"
             "0123456789+/";
 
-        const size_t strBufSize = std::min(d_nextPowerOf2(static_cast<uint32_t>(dataSize/3)), 65536U);
+        const size_t strBufSize = std::min(d_nextPowerOf2(static_cast<uint32_t>(dataSize / 3) + 1), 65536U);
         char* strBuf = static_cast<char*>(std::malloc(strBufSize));
         DISTRHO_SAFE_ASSERT_RETURN(strBuf != nullptr, String());