Improve handling of replacing stream data with empty strings

When an empty string was passed to replaceStreamData, the code was
passing a null pointer to memcpy. Since a 0 size was also passed, this
was harmless, but it triggers sanitizer errors. The code properly
handles a null pointer as the buffer in other places.

1 files changed, 3 insertions, 1 deletions

diff --git a/libqpdf/QPDFObjectHandle.cc b/libqpdf/QPDFObjectHandle.cc
index 10fb153c..4a61f595 100644
--- a/libqpdf/QPDFObjectHandle.cc
+++ b/libqpdf/QPDFObjectHandle.cc
@@ -1468,7 +1468,9 @@ QPDFObjectHandle::replaceStreamData(
     assertStream();
     auto b = std::make_shared<Buffer>(data.length());
     unsigned char* bp = b->getBuffer();
-    memcpy(bp, data.c_str(), data.length());
+    if (bp) {
+        memcpy(bp, data.c_str(), data.length());
+    }
     dynamic_cast<QPDF_Stream*>(obj.get())->replaceStreamData(
         b, filter, decode_parms);
 }