Fix problem when detecting PostGIS version

We are accessing data that doesn't exist if we don't get three
rows from the SQL query.

If the PostGIS version could not be detected, we report that.

Author: joto

src/pgsql-capabilities.cpp

@@ -98,8 +98,16 @@ void init_postgis_version(pg_conn_t const &db_connection)
             capabilities().database_name);
     }
 
-    capabilities().postgis = {std::stoi(std::string{res.get(0, 0)}),
-                              std::stoi(std::string{res.get(1, 0)})};
+    try {
+        if (res.num_tuples() >= 2) {
+            capabilities().postgis = {std::stoi(std::string{res.get(0, 0)}),
+                                      std::stoi(std::string{res.get(1, 0)})};
+            return;
+        }
+    } catch (...) {
+        // Fall through if std::stoi() fails in which case the version
+        // is reported as 0.
+    }
 }
 
 } // anonymous namespace
@@ -114,8 +122,13 @@ void init_database_capabilities(pg_conn_t const &db_connection)
     try {
         log_info("Database version: {}",
                  capabilities().settings.at("server_version"));
-        log_info("PostGIS version: {}.{}", capabilities().postgis.major,
-                 capabilities().postgis.minor);
+
+        if (capabilities().postgis.major == 0) {
+            log_info("PostGIS version: could not be detected");
+        } else {
+            log_info("PostGIS version: {}.{}", capabilities().postgis.major,
+                     capabilities().postgis.minor);
+        }
 
         auto const version_str =
             capabilities().settings.at("server_version_num");