Fix a number of potential or actual static object initialization issues

src/query/plaintorich.cpp

@@ -41,8 +41,6 @@ using std::set;
 #include "cancelcheck.h"
 #include "unacpp.h"
 
-const string PlainToRich::snull = "";
-
 // For debug printing
 static string vecStringToString(const vector<string>& t)
 {

src/query/plaintorich.h

@@ -86,7 +86,7 @@ public:
     virtual string startChunk() {return snull;}
 
 protected:
-    static const string snull;
+    const string snull;
     bool m_inputhtml;
     // Use <br> to break plain text lines (else caller has used a <pre> tag)
     bool m_eolbr;