Do not show prefix in output if there is no metadata.

Previously epubgrep would output “: match” instead of “match”.

Closes: #15

src/output.cpp

@@ -78,22 +78,25 @@ void print_matches(const std::vector<search::match> &matches,
         {
             metadata.emplace_back("page " + match.page);
         }
-        if (!opts.nocolor)
+        if (!metadata.empty())
         {
-            cout << termcolor::italic;
+            if (!opts.nocolor)
-        }
-        for (const auto &part : metadata)
-        {
-            cout << part;
-            if (part != *(metadata.rbegin()))
             {
-                cout << ", ";
+                cout << termcolor::italic;
+            }
+            for (const auto &part : metadata)
+            {
+                cout << part;
+                if (part != *(metadata.rbegin()))
+                {
+                    cout << ", ";
+                }
+            }
+            cout << ": ";
+            if (!opts.nocolor)
+            {
+                cout << termcolor::reset;
             }
-        }
-        cout << ": ";
-        if (!opts.nocolor)
-        {
-            cout << termcolor::reset;
         }
         cout << match.context.first;
         if (!opts.nocolor)