Allow nullptr with zero length in FileAccess get_buffer

fix #47071

(cherry picked from commit c28428fe4dcd78886b972afcad6b239a58b4b973)

core/io/file_access_compressed.cpp

@@ -302,7 +302,7 @@ uint8_t FileAccessCompressed::get_8() const {
 	return ret;
 }
 int FileAccessCompressed::get_buffer(uint8_t *p_dst, int p_length) const {
-	ERR_FAIL_COND_V(!p_dst, -1);
+	ERR_FAIL_COND_V(!p_dst && p_length > 0, -1);
 	ERR_FAIL_COND_V(p_length < 0, -1);
 	ERR_FAIL_COND_V_MSG(!f, -1, "File must be opened before use.");
 	ERR_FAIL_COND_V_MSG(writing, -1, "File has not been opened in read mode.");

core/io/file_access_encrypted.cpp

@@ -233,7 +233,7 @@ uint8_t FileAccessEncrypted::get_8() const {
 }
 
 int FileAccessEncrypted::get_buffer(uint8_t *p_dst, int p_length) const {
-	ERR_FAIL_COND_V(!p_dst, -1);
+	ERR_FAIL_COND_V(!p_dst && p_length > 0, -1);
 	ERR_FAIL_COND_V(p_length < 0, -1);
 	ERR_FAIL_COND_V_MSG(writing, -1, "File has not been opened in read mode.");
 

core/io/file_access_memory.cpp

@@ -150,7 +150,7 @@ uint8_t FileAccessMemory::get_8() const {
 }
 
 int FileAccessMemory::get_buffer(uint8_t *p_dst, int p_length) const {
-	ERR_FAIL_COND_V(!p_dst, -1);
+	ERR_FAIL_COND_V(!p_dst && p_length > 0, -1);
 	ERR_FAIL_COND_V(p_length < 0, -1);
 	ERR_FAIL_COND_V(!data, -1);
 

core/io/file_access_network.cpp

@@ -389,7 +389,7 @@ void FileAccessNetwork::_queue_page(int p_page) const {
 }
 
 int FileAccessNetwork::get_buffer(uint8_t *p_dst, int p_length) const {
-	ERR_FAIL_COND_V(!p_dst, -1);
+	ERR_FAIL_COND_V(!p_dst && p_length > 0, -1);
 	ERR_FAIL_COND_V(p_length < 0, -1);
 
 	//bool eof=false;

core/io/file_access_pack.cpp

@@ -284,7 +284,7 @@ uint8_t FileAccessPack::get_8() const {
 }
 
 int FileAccessPack::get_buffer(uint8_t *p_dst, int p_length) const {
-	ERR_FAIL_COND_V(!p_dst, -1);
+	ERR_FAIL_COND_V(!p_dst && p_length > 0, -1);
 	ERR_FAIL_COND_V(p_length < 0, -1);
 
 	if (eof)

core/io/file_access_zip.cpp

@@ -332,7 +332,7 @@ uint8_t FileAccessZip::get_8() const {
 }
 
 int FileAccessZip::get_buffer(uint8_t *p_dst, int p_length) const {
-	ERR_FAIL_COND_V(!p_dst, -1);
+	ERR_FAIL_COND_V(!p_dst && p_length > 0, -1);
 	ERR_FAIL_COND_V(p_length < 0, -1);
 	ERR_FAIL_COND_V(!zfile, -1);
 	at_eof = unzeof(zfile);

core/os/file_access.cpp

@@ -399,7 +399,7 @@ Vector<String> FileAccess::get_csv_line(const String &p_delim) const {
 }
 
 int FileAccess::get_buffer(uint8_t *p_dst, int p_length) const {
-	ERR_FAIL_COND_V(!p_dst, -1);
+	ERR_FAIL_COND_V(!p_dst && p_length > 0, -1);
 	ERR_FAIL_COND_V(p_length < 0, -1);
 	int i = 0;
 	for (i = 0; i < p_length && !eof_reached(); i++)

drivers/unix/file_access_unix.cpp

@@ -248,7 +248,7 @@ uint8_t FileAccessUnix::get_8() const {
 }
 
 int FileAccessUnix::get_buffer(uint8_t *p_dst, int p_length) const {
-	ERR_FAIL_COND_V(!p_dst, -1);
+	ERR_FAIL_COND_V(!p_dst && p_length > 0, -1);
 	ERR_FAIL_COND_V(p_length < 0, -1);
 	ERR_FAIL_COND_V_MSG(!f, -1, "File must be opened before use.");
 	int read = fread(p_dst, 1, p_length, f);

drivers/windows/file_access_windows.cpp

@@ -259,7 +259,7 @@ uint8_t FileAccessWindows::get_8() const {
 }
 
 int FileAccessWindows::get_buffer(uint8_t *p_dst, int p_length) const {
-	ERR_FAIL_COND_V(!p_dst, -1);
+	ERR_FAIL_COND_V(!p_dst && p_length > 0, -1);
 	ERR_FAIL_COND_V(p_length < 0, -1);
 	ERR_FAIL_COND_V(!f, -1);
 	if (flags == READ_WRITE || flags == WRITE_READ) {