bugfix for empty variable assignment

expr.c

@@ -218,6 +218,7 @@ size_t replaceExpressions(const char* r, char* buffer, size_t buffersize)
     char* w = buffer;
     char* s;
 
+    *w = 0;
     while (*r)
     {
         s = w;

testscript

@@ -87,3 +87,7 @@ x=-0bla -0.1
 x=-2**2 0-2**2 0+-2**2 0--2**2
 # $(x) should be: 4 -4 4 -4
 
+x=
+y=$(x)
+# <$(x)><$(y)> should be: <><>
+