Fix GCC7 warnings.

Taken from upstream:
https://git.savannah.gnu.org/cgit/aspell.git/commit/?id=8089fa02122fed0a6394eba14bbedcb1d18e2384

diff --git a/modules/filter/tex.cpp b/modules/filter/tex.cpp
index a979539..19ab63c 100644
--- a/modules/filter/tex.cpp
+++ b/modules/filter/tex.cpp
@@ -174,7 +174,7 @@ namespace {
 
     if (c == '{') {
 
-      if (top.in_what == Parm || top.in_what == Opt || top.do_check == '\0')
+      if (top.in_what == Parm || top.in_what == Opt || *top.do_check == '\0')
 	push_command(Parm);
 
       top.in_what = Parm;
diff --git a/prog/check_funs.cpp b/prog/check_funs.cpp
index db54f3d..89ee09d 100644
--- a/prog/check_funs.cpp
+++ b/prog/check_funs.cpp
@@ -647,7 +647,7 @@ static void print_truncate(FILE * out, const char * word, int width) {
     }
   }
   if (i == width-1) {
-    if (word == '\0')
+    if (*word == '\0')
       put(out,' ');
     else if (word[len] == '\0')
       put(out, word, len);
td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=214b77b5e749e2ca5891bfc87f946031cf8934e6'>refs</a><a class='active' href='/guix/log/.guix-channel'>log</a><a href='/guix/tree/.guix-channel?id=214b77b5e749e2ca5891bfc87f946031cf8934e6'>tree</a><a href='/guix/commit/.guix-channel?id=214b77b5e749e2ca5891bfc87f946031cf8934e6'>commit</a><a href='/guix/diff/.guix-channel?id=214b77b5e749e2ca5891bfc87f946031cf8934e6'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/.guix-channel'>
<input type='hidden' name='id' value='214b77b5e749e2ca5891bfc87f946031cf8934e6'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=214b77b5e749e2ca5891bfc87f946031cf8934e6'>root</a>/<a href='/guix/log/.guix-channel?id=214b77b5e749e2ca5891bfc87f946031cf8934e6'>.guix-channel</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/.guix-channel?id=214b77b5e749e2ca5891bfc87f946031cf8934e6&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-06-17 19:32:43 +0200'>2020-06-17</span></td><td><a href='/guix/commit/.guix-channel?id=8b1f7c03d239ca703b56f2a6e5f228c79bc1857e'>.guix-channel: Add primary URL.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-06-16 16:10:47 +0200'>2020-06-16</span></td><td><a href='/guix/commit/.guix-channel?id=a941e8fe1f2ef47be2b30a54925febbc7dfb5389'>.guix-channel: Add 'keyring-reference'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-09-23 10:41:30 +0200'>2019-09-23</span></td><td><a href='/guix/commit/.guix-channel?id=dcc90d15581189dbc30e201db2b807273d6484f0'>Add '.guix-channel' file.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>