Use line.reserve in sdobj_ReadFile instead of constructor

Passing a count parameter to the vector constructor does not reserve
count elements but instead fills the vector with count elements.
This caused the endianness check to fail first because the first 256
characters were null bytes.

src/link/sdas_obj.cpp

@@ -136,7 +136,8 @@ enum RelocFlags {
 };
 
 void sdobj_ReadFile(FileStackNode const &where, FILE *file, std::vector<Symbol> &fileSymbols) {
-	std::vector<char> line(256);
+	std::vector<char> line;
+	line.reserve(256);
 	char const *token;
 
 #define getToken(ptr, ...) \