beeversion: Fix output of %X[ex] when X is not dash or underscore

Enforce only prefixing dash or underscore chars when printing
extra{version,name} in %[-_][ex] format strings

fixes https://github.com/bee/bee/issues/207

src/bee_version_output.c

@@ -136,20 +136,21 @@ void print_format(char* s, struct beeversion *v, char *filter_pkgfullname)
                     if(*p == 'A' && *(v->arch))
                         printf(".%s", v->arch);
                     break;
-            }
-            if (*p) {
-                switch(*(p+1)) {
+                case '-':
+                case '_':
+                  switch(*(p+1)) {
                     case 'x':
                         if (*(v->subname))
                             printf("%c%s", *p, v->subname);
                         p++;
-                        continue;
+                        break;
                     case 'e':
                         if (*(v->extraversion))
                             printf("%c%s", *p, v->extraversion);
                         p++;
-                        continue;
-                }
+                        break;
+                  }
+                  break;
             }
             continue;
         } /* if '%' */
@@ -194,4 +195,3 @@ void print_format(char* s, struct beeversion *v, char *filter_pkgfullname)
 
     } /* for *p */
 }
-